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Structural and biochemical insights into 2′-O-methylation at the 3′-terminal nucleotide of RNA by Hen1

Mui Chan, Chio; Zhou, Chun; Brunzelle, Joseph S.; Huang, Raven H.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Small RNAs of ≈20–30 nt have diverse and important biological roles in eukaryotic organisms. After being generated by Dicer or Piwi proteins, all small RNAs in plants and a subset of small RNAs in animals are further modified at their 3′-terminal nucleotides via 2′-O-methylation, carried out by the S-adenosylmethionine-dependent methyltransferase (MTase) Hen1. Methylation at the 3′ terminus is vital for biological functions of these small RNAs. Here, we report four crystal structures of the MTase domain of a bacterial homolog of Hen1 from Clostridium thermocellum and Anabaena variabilis, which are enzymatically indistinguishable from the eukaryotic Hen1 in their ability to methylate small single-stranded RNAs. The structures reveal that, in addition to the core fold of the MTase domain shared by other RNA and DNA MTases, the MTase domain of Hen1 possesses a motif and a domain that are highly conserved and are unique to Hen1. The unique motif and domain are likely to be involved in RNA substrate recognition and catalysis. The structures allowed us to construct a docking model of an RNA substrate bound to the MTase domain of bacterial Hen1, which is likely similar to that of the eukaryotic counterpart. The model, supported by mutational studies...

Adaptive response by state-dependent inactivation

Friedlander, Tamar; Brenner, Naama
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Many membrane channels and receptors exhibit adaptive, or desensitized, response to a strong sustained input stimulus. A key mechanism that underlies this response is the slow, activity-dependent removal of responding molecules to a pool which is unavailable to respond immediately to the input. This mechanism is implemented in different ways in various biological systems and has traditionally been studied separately for each. Here we highlight the common aspects of this principle, shared by many biological systems, and suggest a unifying theoretical framework. We study theoretically a class of models which describes the general mechanism and allows us to distinguish its universal from system-specific features. We show that under general conditions, regardless of the details of kinetics, molecule availability encodes an averaging over past activity and feeds back multiplicatively on the system output. The kinetics of recovery from unavailability determines the effective memory kernel inside the feedback branch, giving rise to a variety of system-specific forms of adaptive response—precise or input-dependent, exponential or power-law—as special cases of the same model.

A circadian clock in Saccharomyces cerevisiae

Eelderink-Chen, Zheng; Mazzotta, Gabriella; Sturre, Marcel; Bosman, Jasper; Roenneberg, Till; Merrow, Martha
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Circadian timing is a fundamental biological process, underlying cellular physiology in animals, plants, fungi, and cyanobacteria. Circadian clocks organize gene expression, metabolism, and behavior such that they occur at specific times of day. The biological clocks that orchestrate these daily changes confer a survival advantage and dominate daily behavior, for example, waking us in the morning and helping us to sleep at night. The molecular mechanism of circadian clocks has been sketched out in genetic model systems from prokaryotes to humans, revealing a combination of transcriptional and posttranscriptional pathways, but the clock mechanism is far from solved. Although Saccharomyces cerevisiae is among the most powerful genetic experimental systems and, as such, could greatly contribute to our understanding of cellular timing, it still remains absent from the repertoire of circadian model organisms. Here, we use continuous cultures of yeast, establishing conditions that reveal characteristic clock properties similar to those described in other species. Our results show that metabolism in yeast shows systematic circadian entrainment, responding to cycle length and zeitgeber (stimulus) strength, and a (heavily damped) free running rhythm. Furthermore...

Surface-coupled proton exchange of a membrane-bound proton acceptor

Sandén, Tor; Salomonsson, Lina; Brzezinski, Peter; Widengren, Jerker
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Proton-transfer reactions across and at the surface of biological membranes are central for maintaining the transmembrane proton electrochemical gradients involved in cellular energy conversion. In this study, fluorescence correlation spectroscopy was used to measure the local protonation and deprotonation rates of single pH-sensitive fluorophores conjugated to liposome membranes, and the dependence of these rates on lipid composition and ion concentration. Measurements of proton exchange rates over a wide proton concentration range, using two different pH-sensitive fluorophores with different pKas, revealed two distinct proton exchange regimes. At high pH (> 8), proton association increases rapidly with increasing proton concentrations, presumably because the whole membrane acts as a proton-collecting antenna for the fluorophore. In contrast, at low pH (< 7), the increase in the proton association rate is slower and comparable to that of direct protonation of the fluorophore from the bulk solution. In the latter case, the proton exchange rates of the two fluorophores are indistinguishable, indicating that their protonation rates are determined by the local membrane environment. Measurements on membranes of different surface charge and at different ion concentrations made it possible to determine surface potentials...

Minute negative superhelicity is sufficient to induce the B-Z transition in the presence of low tension

Lee, Mina; Kim, Sook Ho; Hong, Seok-Cheol
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Left-handed Z-DNA has fascinated biological scientists for decades by its extraordinary structure and potential involvement in biological phenomena. Despite its instability relative to B-DNA, Z-DNA is stabilized in vivo by negative supercoiling. A detailed understanding of Z-DNA formation is, however, still lacking. In this study, we have examined the B-Z transition in a short guanine/cytosine (GC) repeat in the presence of controlled tension and superhelicity via a hybrid technique of single-molecule FRET and magnetic tweezers. The hybrid scheme enabled us to identify the states of the specific GC region under mechanical control and trace conformational changes synchronously at local and global scales. Intriguingly, minute negative superhelicity can facilitate the B-Z transition at low tension, indicating that tension, as well as torsion, plays a pivotal role in the transition. Dynamic interconversions between the states at elevated temperatures yielded thermodynamic and kinetic constants of the transition. Our single-molecule studies shed light on the understanding of Z-DNA formation by highlighting the highly cooperative and dynamic nature of the B-Z transition.

Interactome analysis of longitudinal pharyngeal infection of cynomolgus macaques by group A Streptococcus

Shea, Patrick R.; Virtaneva, Kimmo; Kupko, John J.; Porcella, Stephen F.; Barry, William T.; Wright, Fred A.; Kobayashi, Scott D.; Carmody, Aaron; Ireland, Robin M.; Sturdevant, Daniel E.; Ricklefs, Stacy M.; Babar, Imran; Johnson, Claire A.; Graham, Mora
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Relatively little is understood about the dynamics of global host–pathogen transcriptome changes that occur during bacterial infection of mucosal surfaces. To test the hypothesis that group A Streptococcus (GAS) infection of the oropharynx provokes a distinct host transcriptome response, we performed genome-wide transcriptome analysis using a nonhuman primate model of experimental pharyngitis. We also identified host and pathogen biological processes and individual host and pathogen gene pairs with correlated patterns of expression, suggesting interaction. For this study, 509 host genes and seven biological pathways were differentially expressed throughout the entire 32-day infection cycle. GAS infection produced an initial widespread significant decrease in expression of many host genes, including those involved in cytokine production, vesicle formation, metabolism, and signal transduction. This repression lasted until day 4, at which time a large increase in expression of host genes was observed, including those involved in protein translation, antigen presentation, and GTP-mediated signaling. The interactome analysis identified 73 host and pathogen gene pairs with correlated expression levels. We discovered significant correlations between transcripts of GAS genes involved in hyaluronic capsule production and host endocytic vesicle formation...

Neurons sense nanoscale roughness with nanometer sensitivity

Brunetti, V.; Maiorano, G.; Rizzello, L.; Sorce, B.; Sabella, S.; Cingolani, R.; Pompa, P. P.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The interaction between cells and nanostructured materials is attracting increasing interest, because of the possibility to open up novel concepts for the design of smart nanobiomaterials with active biological functionalities. In this frame we investigated the response of human neuroblastoma cell line (SH-SY5Y) to gold surfaces with different levels of nanoroughness. To achieve a precise control of the nanoroughness with nanometer resolution, we exploited a wet chemistry approach based on spontaneous galvanic displacement reaction. We demonstrated that neurons sense and actively respond to the surface nanotopography, with a surprising sensitivity to variations of few nanometers. We showed that focal adhesion complexes, which allow cellular sensing, are strongly affected by nanostructured surfaces, leading to a marked decrease in cell adhesion. Moreover, cells adherent on nanorough surfaces exhibit loss of neuron polarity, Golgi apparatus fragmentation, nuclear condensation, and actin cytoskeleton that is not functionally organized. Apoptosis/necrosis assays established that nanoscale features induce cell death by necrosis, with a trend directly related to roughness values. Finally, by seeding SH-SY5Y cells onto micropatterned flat and nanorough gold surfaces...

Scaling of morphogen gradients by an expansion-repression integral feedback control

Ben-Zvi, Danny; Barkai, Naama
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Despite substantial size variations, proportions of the developing body plan are maintained with a remarkable precision. Little is known about the mechanisms that ensure this adaptation (scaling) of pattern with size. Most models of patterning by morphogen gradients do not support scaling. In contrast, we show that scaling arises naturally in a general feedback topology, in which the range of the morphogen gradient increases with the abundance of some diffusible molecule, whose production, in turn, is repressed by morphogen signaling. We term this mechanism “expansion–repression” and show that it can function within a wide range of biological scenarios. The expansion-repression scaling mechanism is analogous to an integral-feedback controller, a key concept in engineering that is likely to be instrumental also in maintaining biological homeostasis.

Archaeopteryx feathers and bone chemistry fully revealed via synchrotron imaging

Bergmann, U.; Morton, R. W.; Manning, P. L.; Sellers, W. I.; Farrar, S.; Huntley, K. G.; Wogelius, R. A.; Larson, P.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Evolution of flight in maniraptoran dinosaurs is marked by the acquisition of distinct avian characters, such as feathers, as seen in Archaeopteryx from the Solnhofen limestone. These rare fossils were pivotal in confirming the dinosauria-avian lineage. One of the key derived avian characters is the possession of feathers, details of which were remarkably preserved in the Lagerstätte environment. These structures were previously simply assumed to be impressions; however, a detailed chemical analysis has, until now, never been completed on any Archaeopteryx specimen. Here we present chemical imaging via synchrotron rapid scanning X-ray fluorescence (SRS-XRF) of the Thermopolis Archaeopteryx, which shows that portions of the feathers are not impressions but are in fact remnant body fossil structures, maintaining elemental compositions that are completely different from the embedding geological matrix. Our results indicate phosphorous and sulfur retention in soft tissue as well as trace metal (Zn and Cu) retention in bone. Other previously unknown chemical details of Archaeopteryx are also revealed in this study including: bone chemistry, taphonomy (fossilization process), and curation artifacts. SRS-XRF represents a major advancement in the study of the life chemistry and fossilization processes of Archaeopteryx and other extinct organisms because it is now practical to image the chemistry of large specimens rapidly at concentration levels of parts per million. This technique has wider application to the archaeological...

Comparing genomes to computer operating systems in terms of the topology and evolution of their regulatory control networks

Yan, Koon-Kiu; Fang, Gang; Bhardwaj, Nitin; Alexander, Roger P.; Gerstein, Mark
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The genome has often been called the operating system (OS) for a living organism. A computer OS is described by a regulatory control network termed the call graph, which is analogous to the transcriptional regulatory network in a cell. To apply our firsthand knowledge of the architecture of software systems to understand cellular design principles, we present a comparison between the transcriptional regulatory network of a well-studied bacterium (Escherichia coli) and the call graph of a canonical OS (Linux) in terms of topology and evolution. We show that both networks have a fundamentally hierarchical layout, but there is a key difference: The transcriptional regulatory network possesses a few global regulators at the top and many targets at the bottom; conversely, the call graph has many regulators controlling a small set of generic functions. This top-heavy organization leads to highly overlapping functional modules in the call graph, in contrast to the relatively independent modules in the regulatory network. We further develop a way to measure evolutionary rates comparably between the two networks and explain this difference in terms of network evolution. The process of biological evolution via random mutation and subsequent selection tightly constrains the evolution of regulatory network hubs. The call graph...

Structure of the histone chaperone CIA/ASF1–double bromodomain complex linking histone modifications and site-specific histone eviction

Akai, Yusuke; Adachi, Naruhiko; Hayashi, Yohei; Eitoku, Masamitsu; Sano, Norihiko; Natsume, Ryo; Kudo, Norio; Tanokura, Masaru; Senda, Toshiya; Horikoshi, Masami
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Nucleosomes around the promoter region are disassembled for transcription in response to various signals, such as acetylation and methylation of histones. Although the interactions between histone-acetylation-recognizing bromodomains and factors involved in nucleosome disassembly have been reported, no structural basis connecting histone modifications and nucleosome disassembly has been obtained. Here, we determined at 3.3 Å resolution the crystal structure of histone chaperone cell cycle gene 1 (CCG1) interacting factor A/antisilencing function 1 (CIA/ASF1) in complex with the double bromodomain in the CCG1/TAF1/TAF(II)250 subunit of transcription factor IID. Structural, biochemical, and biological studies suggested that interaction between double bromodomain and CIA/ASF1 is required for their colocalization, histone eviction, and pol II entry at active promoter regions. Furthermore, the present crystal structure has characteristics that can connect histone acetylation and CIA/ASF1-mediated histone eviction. These findings suggest that the molecular complex between CIA/ASF1 and the double bromodomain plays a key role in site-specific histone eviction at active promoter regions. The model we propose here is the initial structure-based model of the biological signaling from histone modifications to structural change of the nucleosome (hi-MOST model).

Imprints of the genetic code in the ribosome

Johnson, David B. F.; Wang, Lei
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The establishment of the genetic code remains elusive nearly five decades after the code was elucidated. The stereochemical hypothesis postulates that the code developed from interactions between nucleotides and amino acids, yet supporting evidence in a biological context is lacking. We show here that anticodons are selectively enriched near their respective amino acids in the ribosome, and that such enrichment is significantly correlated with the canonical code over random codes. Ribosomal anticodon-amino acid enrichment further reveals that specific codons were reassigned during code evolution, and that the code evolved through a two-stage transition from ancient amino acids without anticodon interaction to newer additions with anticodon interaction. The ribosome thus serves as a molecular fossil, preserving biological evidence that anticodon-amino acid interactions shaped the evolution of the genetic code.

Downsizing human, bacterial, and viral proteins to short water-stable alpha helices that maintain biological potency

Harrison, Rosemary S.; Shepherd, Nicholas E.; Hoang, Huy N.; Ruiz-Gómez, Gloria; Hill, Timothy A.; Driver, Russell W.; Desai, Vishal S.; Young, Paul R.; Abbenante, Giovanni; Fairlie, David P.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Recombinant proteins are important therapeutics due to potent, highly specific, and nontoxic actions in vivo. However, they are expensive medicines to manufacture, chemically unstable, and difficult to administer with low patient uptake and compliance. Small molecule drugs are cheaper and more bioavailable, but less target-specific in vivo and often have associated side effects. Here we combine some advantages of proteins and small molecules by taking short amino acid sequences that confer potency and selectivity to proteins, and fixing them as small constrained molecules that are chemically and structurally stable and easy to make. Proteins often use short α-helices of just 1–4 helical turns (4–15 amino acids) to interact with biological targets, but peptides this short usually have negligible α-helicity in water. Here we show that short peptides, corresponding to helical epitopes from viral, bacterial, or human proteins, can be strategically fixed in highly α-helical structures in water. These helix-constrained compounds have similar biological potencies as proteins that bear the same helical sequences. Examples are (i) a picomolar inhibitor of Respiratory Syncytial Virus F protein mediated fusion with host cells, (ii) a nanomolar inhibitor of RNA binding to the transporter protein HIV-Rev...

A general basis for quarter-power scaling in animals

Banavar, Jayanth R.; Moses, Melanie E.; Brown, James H.; Damuth, John; Rinaldo, Andrea; Sibly, Richard M.; Maritan, Amos
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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It has been known for decades that the metabolic rate of animals scales with body mass with an exponent that is almost always <1, >2/3, and often very close to 3/4. The 3/4 exponent emerges naturally from two models of resource distribution networks, radial explosion and hierarchically branched, which incorporate a minimum of specific details. Both models show that the exponent is 2/3 if velocity of flow remains constant, but can attain a maximum value of 3/4 if velocity scales with its maximum exponent, 1/12. Quarter-power scaling can arise even when there is no underlying fractality. The canonical “fourth dimension” in biological scaling relations can result from matching the velocity of flow through the network to the linear dimension of the terminal “service volume” where resources are consumed. These models have broad applicability for the optimal design of biological and engineered systems where energy, materials, or information are distributed from a single source.

Inducible expression eliminates the fitness cost of vancomycin resistance in enterococci

Foucault, Marie-Laure; Depardieu, Florence; Courvalin, Patrice; Grillot-Courvalin, Catherine
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Inducible vancomycin resistance in enterococci is due to a sophisticated mechanism that combines synthesis of cell wall peptidoglycan precursors with low affinity for glycopeptides and elimination of the normal target precursors. Although this dual mechanism, which involves seven genes organized in two operons, is predicted to have a high fitness cost, resistant enterococci have disseminated worldwide. We have evaluated the biological cost of VanB-type resistance due to acquisition of conjugative transposon Tn1549 in Enterococcus faecium and Enterococcus faecalis. Because fitness was dependent on the integration site of Tn1549, an isogenic set of E. faecalis was constructed to determine the cost of inducible or constitutive expression of resistance or of carriage of Tn1549. A luciferase gene was inserted in the integrase gene of the transposon to allow differential quantification of the strains in cocultures and in the digestive tract of gnotobiotic mice. Both in vitro and in vivo, carriage of inactivated or inducible Tn1549 had no cost for the host in the absence of induction by vancomycin. In contrast, induced or constitutively resistant strains not only had reduced fitness but were severely impaired in colonization ability and dissemination among mice. These data indicate that tight regulation of resistance expression drastically reduces the biological cost associated with vancomycin resistance in Enterococcus spp. and accounts for the widespread dissemination of these strains. Our findings are in agreement with the observation that regulation of expression is common in horizontally acquired resistance and represents an efficient evolutionary pathway for resistance determinants to become selectively neutral.

Probability landscape of heritable and robust epigenetic state of lysogeny in phage lambda

Cao, Youfang; Lu, Hsiao-Mei; Liang, Jie
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Computational studies of biological networks can help to identify components and wirings responsible for observed phenotypes. However, studying stochastic networks controlling many biological processes is challenging. Similar to Schrödinger’s equation in quantum mechanics, the chemical master equation (CME) provides a basic framework for understanding stochastic networks. However, except for simple problems, the CME cannot be solved analytically. Here we use a method called discrete chemical master equation (dCME) to compute directly the full steady-state probability landscape of the lysogeny maintenance network in phage lambda from its CME. Results show that wild-type phage lambda can maintain a constant level of repressor over a wide range of repressor degradation rate and is stable against UV irradiation, ensuring heritability of the lysogenic state. Furthermore, it can switch efficiently to the lytic state once repressor degradation increases past a high threshold by a small amount. We find that beyond bistability and nonlinear dimerization, cooperativity between repressors bound to OR1 and OR2 is required for stable and heritable epigenetic state of lysogeny that can switch efficiently. Mutants of phage lambda lack stability and do not possess a high threshold. Instead...

Invasive honeysuckle eradication reduces tick-borne disease risk by altering host dynamics

Allan, Brian F.; Dutra, Humberto P.; Goessling, Lisa S.; Barnett, Kirk; Chase, Jonathan M.; Marquis, Robert J.; Pang, Genevieve; Storch, Gregory A.; Thach, Robert E.; Orrock, John L.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Despite the ubiquity of invasive organisms and their often deleterious effects on native flora and fauna, the consequences of biological invasions for human health and the ecological mechanisms through which they occur are rarely considered. Here we demonstrate that a widespread invasive shrub in North America, Amur honeysuckle (Lonicera maackii), increases human risk of exposure to ehrlichiosis, an emerging infectious disease caused by bacterial pathogens transmitted by the lone star tick (Amblyomma americanum). Using large-scale observational surveys in natural areas across the St. Louis, Missouri region, we found that white-tailed deer (Odocoileus virginianus), a preeminent tick host and pathogen reservoir, more frequently used areas invaded by honeysuckle. This habitat preference translated into considerably greater numbers of ticks infected with pathogens in honeysuckle-invaded areas relative to adjacent honeysuckle-uninvaded areas. We confirmed this biotic mechanism using an experimental removal of honeysuckle, which caused a decrease in deer activity and infected tick numbers, as well as a proportional shift in the blood meals of ticks away from deer. We conclude that disease risk is likely to be reduced when honeysuckle is eradicated...

Single amino acid change alters the ability to specify male or female organ identity

Airoldi, Chiara A.; Bergonzi, Sara; Davies, Brendan
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The molecular mechanisms underlying the developmental processes that shape living organisms provide a basis to understand the evolution of biological complexity. Gene duplication allows biological functions to become separated, leading to increased complexity through subfunctionalization. Recently, the relative contributions to morphological evolution of changes to the regulatory and/or coding regions of duplicated genes have been the subject of debate. Duplication generated multiple copies of the MADS-box transcription factor genes that play essential roles in specifying organ identity in the flower, making this evolutionary novelty a good model to investigate the nature of the changes necessary to drive subfunctionalization. Here, we show that naturally occurring variation at a single amino acid in a MADS-box transcription factor switches its ability to specify male and female reproductive organs by altering its repertoire of protein–protein interactions. However, these different developmental fates are only manifest because of an underlying variation in the expression pattern of interacting proteins. This shows that the morphological outcomes of changes to protein sequence and gene expression must be interpreted in the context of the wider regulatory network. It also suggests an explanation for the surprisingly widespread duplications of some of the floral transcription factors.

Arginine methylation mediated by the Arabidopsis homolog of PRMT5 is essential for proper pre-mRNA splicing

Deng, Xian; Gu, Lianfeng; Liu, Chunyan; Lu, Tiancong; Lu, Falong; Lu, Zhike; Cui, Peng; Pei, Yanxi; Wang, Baichen; Hu, Songnian; Cao, Xiaofeng
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Protein arginine methylation, one of the most abundant and important posttranslational modifications, is involved in a multitude of biological processes in eukaryotes, such as transcriptional regulation and RNA processing. Symmetric arginine dimethylation is required for snRNP biogenesis and is assumed to be essential for pre-mRNA splicing; however, except for in vitro evidence, whether it affects splicing in vivo remains elusive. Mutation in an Arabidopsis symmetric arginine dimethyltransferase, AtPRMT5, causes pleiotropic developmental defects, including late flowering, but the underlying molecular mechanism is largely unknown. Here we show that AtPRMT5 methylates a wide spectrum of substrates, including some RNA binding or processing factors and U snRNP AtSmD1, D3, and AtLSm4 proteins, which are involved in RNA metabolism. RNA-seq analyses reveal that AtPRMT5 deficiency causes splicing defects in hundreds of genes involved in multiple biological processes. The splicing defects are identified in transcripts of several RNA processing factors involved in regulating flowering time. In particular, splicing defects at the flowering regulator FLOWERING LOCUS KH DOMAIN (FLK) in atprmt5 mutants reduce its functional transcript and protein levels...

HIV-1 viral infectivity factor interacts with TP53 to induce G2 cell cycle arrest and positively regulate viral replication

Izumi, Taisuke; Io, Katsuhiro; Matsui, Masashi; Shirakawa, Kotaro; Shinohara, Masanobu; Nagai, Yuya; Kawahara, Masahiro; Kobayashi, Masayuki; Kondoh, Hiroshi; Misawa, Naoko; Koyanagi, Yoshio; Uchiyama, Takashi; Takaori-Kondo, Akifumi
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Viral infectivity factor, an accessory protein encoded in the HIV-1 genome, induces G2 cell cycle arrest; however, the biological significance and mechanism(s) remain totally unclear. Here we demonstrate that the TP53 pathway is involved in Vif-mediated G2 cell cycle arrest. Vif enhances the stability and transcriptional activity of TP53 by blocking the MDM2-mediated ubiquitination and nuclear export of TP53. Furthermore, Vif causes G2 cell cycle arrest in a TP53-dependent manner. HXB2 Vif lacks these activities toward TP53 and cannot induce G2 cell cycle arrest. Using mutagenesis, we demonstrate that the critical residues for this function are located in the N-terminal region of Vif. Finally, we construct a mutant NL4-3 virus with an NL4-3/HXB2 chimeric Vif defective for the ability to induce cell cycle arrest and show that the mutant virus replicates less effectively than the wild-type NL4-3 virus in T cells expressing TP53. These data imply that Vif induces G2 cell cycle arrest through functional interaction with the TP53/MDM2 axis and that the G2 cell cycle arrest induced by Vif has a positive effect on HIV-1 replication. This report demonstrates the molecular mechanisms and the biological significance of Vif-mediated G2 cell cycle arrest for HIV-1 infection.