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Stavropoulou A, Tassios E, Kalyva M, Georgoulopoulos M, Vakirlis N, Iliopoulos I, Nikolaou C. Distinct chromosomal “niches” in the genome of Saccharomyces cerevisiae provide the background for genomic innovation and shape the fate of gene duplicates. NAR Genom Bioinform 2022; 4:lqac086. [PMID: 36381424 PMCID: PMC9661399 DOI: 10.1093/nargab/lqac086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2022] [Revised: 10/20/2022] [Accepted: 10/25/2022] [Indexed: 11/15/2022] Open
Abstract
Nearly one third of Saccharomyces cerevisiae protein coding sequences correspond to duplicate genes, equally split between small-scale duplicates (SSD) and whole-genome duplicates (WGD). While duplicate genes have distinct properties compared to singletons, to date, there has been no systematic analysis of their positional preferences. In this work, we show that SSD and WGD genes are organized in distinct gene clusters that occupy different genomic regions, with SSD being more peripheral and WGD more centrally positioned close to centromeric chromatin. Duplicate gene clusters differ from the rest of the genome in terms of gene size and spacing, gene expression variability and regulatory complexity, properties that are also shared by singleton genes residing within them. Singletons within duplicate gene clusters have longer promoters, more complex structure and a higher number of protein–protein interactions. Particular chromatin architectures appear to be important for gene evolution, as we find SSD gene-pair co-expression to be strongly associated with the similarity of nucleosome positioning patterns. We propose that specific regions of the yeast genome provide a favourable environment for the generation and maintenance of small-scale gene duplicates, segregating them from WGD-enriched genomic domains. Our findings provide a valuable framework linking genomic innovation with positional genomic preferences.
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Affiliation(s)
- Athanasia Stavropoulou
- Medical School, University of Crete , Heraklion 70013, Greece
- Computational Genomics Group, Biomedical Sciences Research Center “Alexander Fleming” , Athens 16672, Greece
| | - Emilios Tassios
- Medical School, University of Crete , Heraklion 70013, Greece
- Computational Genomics Group, Biomedical Sciences Research Center “Alexander Fleming” , Athens 16672, Greece
| | - Maria Kalyva
- European Bioinformatics Institute, EMBL-EBI, Wellcome Genome Campus , Hinxton, Cambridgeshire, CB10 1SD, UK
| | | | - Nikolaos Vakirlis
- Computational Genomics Group, Biomedical Sciences Research Center “Alexander Fleming” , Athens 16672, Greece
| | | | - Christoforos Nikolaou
- Computational Genomics Group, Biomedical Sciences Research Center “Alexander Fleming” , Athens 16672, Greece
- Hellenic Open University , Patras 26335, Greece
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Farahani RM, Rezaei-Lotfi S, Hunter N. Genomic competition for noise reduction shaped evolutionary landscape of mir-4673. NPJ Syst Biol Appl 2020; 6:12. [PMID: 32376854 PMCID: PMC7203229 DOI: 10.1038/s41540-020-0131-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 04/09/2020] [Indexed: 12/24/2022] Open
Abstract
The genomic platform that informs evolution of microRNA cascades remains unknown. Here we capitalised on the recent evolutionary trajectory of hominin-specific miRNA-4673, encoded in intron 4 of notch-1, to uncover the identity of one such precursor genomic element and the selective forces acting upon it. The miRNA targets genes that regulate Wnt/β-catenin signalling cascade. Primary sequence of the microRNA and its target region in Wnt modulating genes evolved from homologous signatures mapped to homotypic cis-clusters recognised by TCF3/4 and TFAP2A/B/C families. Integration of homologous TFAP2A/B/C cis-clusters (short range inhibitor of β-catenin) into the transcriptional landscape of Wnt cascade genes can reduce noise in gene expression. Probabilistic adoption of miRNA secondary structure by one such cis-signature in notch-1 reflected selection for superhelical curvature symmetry of precursor DNA to localise a nucleosome that overlapped the latter cis-cluster. By replicating the cis-cluster signature, non-random interactions of the miRNA with key Wnt modulator genes expanded the transcriptional noise buffering capacity via a coherent feed-forward loop mechanism. In consequence, an autonomous transcriptional noise dampener (the cis-cluster/nucleosome) evolved into a post-transcriptional one (the miRNA). The findings suggest a latent potential for remodelling of transcriptional landscape by miRNAs that capitalise on non-random distribution of genomic cis-signatures.
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Affiliation(s)
- Ramin M Farahani
- IDR/Westmead Institute for Medical Research and Westmead Centre for Oral Health, Sydney, NSW, Australia.
- Faculty of Medicine and Health Sciences, University of Sydney, Sydney, NSW, 2006, Australia.
| | - Saba Rezaei-Lotfi
- Faculty of Medicine and Health Sciences, University of Sydney, Sydney, NSW, 2006, Australia
| | - Neil Hunter
- IDR/Westmead Institute for Medical Research and Westmead Centre for Oral Health, Sydney, NSW, Australia
- Faculty of Medicine and Health Sciences, University of Sydney, Sydney, NSW, 2006, Australia
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Tahir M, Hayat M, Khan SA. iNuc-ext-PseTNC: an efficient ensemble model for identification of nucleosome positioning by extending the concept of Chou's PseAAC to pseudo-tri-nucleotide composition. Mol Genet Genomics 2018; 294:199-210. [PMID: 30291426 DOI: 10.1007/s00438-018-1498-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 09/28/2018] [Indexed: 10/28/2022]
Abstract
Nucleosome is a central element of eukaryotic chromatin, which composes of histone proteins and DNA molecules. It performs vital roles in many eukaryotic intra-nuclear processes, for instance, chromatin structure and transcriptional regulation formation. Identification of nucleosome positioning via wet lab is difficult; so, the attention is diverted towards the accurate intelligent automated prediction. In this regard, a novel intelligent automated model "iNuc-ext-PseTNC" is developed to identify the nucleosome positioning in genomes accurately. In this predictor, the sequences of DNA are mathematically represented by two different discrete feature extraction techniques, namely pseudo-tri-nucleotide composition (PseTNC) and pseudo-di-nucleotide composition. Several contemporary machine learning algorithms were examined. Further, the predictions of individual classifiers were integrated through an evolutionary genetic algorithm. The success rates of the ensemble model are higher than individual classifiers. After analyzing the prediction results, it is noticed that iNuc-ext-PseTNC model has achieved better performance in combination with PseTNC feature space, which are 94.3%, 93.14%, and 88.60% of accuracies using six-fold cross-validation test for the three benchmark datasets S1, S2, and S3, respectively. The achieved outcomes exposed that the results of iNuc-ext-PseTNC model are prominent compared to the existing methods so far notifiable in the literature. It is ascertained that the proposed model might be more fruitful and a practical tool for rudimentary academia and research.
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Affiliation(s)
- Muhammad Tahir
- Department of Computer Science, Abdul Wali Khan University Mardan, Mardan, KP, Pakistan
| | - Maqsood Hayat
- Department of Computer Science, Abdul Wali Khan University Mardan, Mardan, KP, Pakistan.
| | - Sher Afzal Khan
- Department of Computer Science, Abdul Wali Khan University Mardan, Mardan, KP, Pakistan
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Bameta T, Das D, Padinhateeri R. Coupling of replisome movement with nucleosome dynamics can contribute to the parent-daughter information transfer. Nucleic Acids Res 2018; 46:4991-5000. [PMID: 29850895 PMCID: PMC6007630 DOI: 10.1093/nar/gky207] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 03/09/2018] [Indexed: 01/09/2023] Open
Abstract
Positioning of nucleosomes along the genomic DNA is crucial for many cellular processes that include gene regulation and higher order packaging of chromatin. The question of how nucleosome-positioning information from a parent chromatin gets transferred to the daughter chromatin is highly intriguing. Accounting for experimentally known coupling between replisome movement and nucleosome dynamics, we propose a model that can obtain de novo nucleosome assembly similar to what is observed in recent experiments. Simulating nucleosome dynamics during replication, we argue that short pausing of the replication fork, associated with nucleosome disassembly, can be a event crucial for communicating nucleosome positioning information from parent to daughter. We show that the interplay of timescales between nucleosome disassembly (τp) at the replication fork and nucleosome sliding behind the fork (τs) can give rise to a rich ‘phase diagram’ having different inherited patterns of nucleosome organization. Our model predicts that only when τp ≥ τs the daughter chromatin can inherit nucleosome positioning of the parent.
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Affiliation(s)
- Tripti Bameta
- UM-DAE Centre for Excellence in Basic Sciences, University of Mumbai, Vidhyanagari Campus, Mumbai 400098, India
- To whom correspondence should be addressed. Tel: +91 22 25767761; Fax: +91 22 25767760; . Correspondence may also be addressed to Tripti Bameta.
| | - Dibyendu Das
- Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Ranjith Padinhateeri
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India
- To whom correspondence should be addressed. Tel: +91 22 25767761; Fax: +91 22 25767760; . Correspondence may also be addressed to Tripti Bameta.
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Nikolaou C. Invisible cities: segregated domains in the yeast genome with distinct structural and functional attributes. Curr Genet 2017; 64:247-258. [PMID: 28780612 DOI: 10.1007/s00294-017-0731-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 07/31/2017] [Accepted: 08/02/2017] [Indexed: 02/07/2023]
Abstract
Recent advances in our understanding of the three-dimensional organization of the eukaryotic nucleus have rendered the spatial distribution of genes increasingly relevant. In a recent work (Tsochatzidou et al., Nucleic Acids Res 45:5818-5828, 2017), we proposed the existence of a functional compartmentalization of the yeast genome according to which, genes occupying the chromosomal regions at the nuclear periphery have distinct structural, functional and evolutionary characteristics compared to their centromeric-proximal counterparts. Around the same time, it was also shown that the genome of Saccharomyces cerevisiae is organized in topologically associated domains (TADs), which are largely associated with the replication timing. In this work, we proceed to investigate whether such units of three-dimensional genomic organization can be linked to transcriptional activity as a driving force for the shaping of genomic architecture. Through the application of a simple boundary-calling criterion in genome-wide 3C data, we define ~100 TAD-like domains which can be clustered in six different classes with radically different nucleosomal organizations, significant variations in transcription factor binding and uneven chromosomal distribution. Approximately ~20% of the genome is found to be confined in regions with "closed" chromatin structure around gene promoters. Most interestingly, we find both "open" and "closed" regions to be segregated, in the sense that they tend to avoid inter-chromosomal interactions. Our data further enforce the notion of a marked compartmentalization of the yeast genome in isolated territories, with implications in its function and evolution.
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Affiliation(s)
- Christoforos Nikolaou
- Computational Genomics Group, Department of Biology, University of Crete, 70013, Herakleion, Greece.
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Awazu A. Prediction of nucleosome positioning by the incorporation of frequencies and distributions of three different nucleotide segment lengths into a general pseudo k-tuple nucleotide composition. Bioinformatics 2016; 33:42-48. [PMID: 27563027 PMCID: PMC5860184 DOI: 10.1093/bioinformatics/btw562] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Revised: 08/02/2016] [Accepted: 08/19/2016] [Indexed: 11/13/2022] Open
Abstract
Motivation Nucleosome positioning plays important roles in many eukaryotic intranuclear processes, such as transcriptional regulation and chromatin structure formation. The investigations of nucleosome positioning rules provide a deeper understanding of these intracellular processes. Results Nucleosome positioning prediction was performed using a model consisting of three types of variables characterizing a DNA sequence—the number of five-nucleotide sequences, the number of three-nucleotide combinations in one period of a helix, and mono- and di-nucleotide distributions in DNA fragments. Using recently proposed stringent benchmark datasets with low biases for Saccharomyces cerevisiae, Homo sapiens, Caenorhabditis elegans and Drosophila melanogaster, the present model was shown to have a better prediction performance than the recently proposed predictors. This model was able to display the common and organism-dependent factors that affect nucleosome forming and inhibiting sequences as well. Therefore, the predictors developed here can accurately predict nucleosome positioning and help determine the key factors influencing this process. Supplementary information Supplementary data are available at Bioinformatics online.
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Affiliation(s)
- Akinori Awazu
- Department of Mathematical and Life Sciences.,Research Center for Mathematics on Chromatin Live Dynamics, Hiroshima University, Kagami-yama 1-3-1, Higashi-Hiroshima, 739-8526, Japan
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Abstract
Nucleosome positioning is an important process required for proper genome packing and its accessibility to execute the genetic program in a cell-specific, timely manner. In the recent years hundreds of papers have been devoted to the bioinformatics, physics and biology of nucleosome positioning. The purpose of this review is to cover a practical aspect of this field, namely, to provide a guide to the multitude of nucleosome positioning resources available online. These include almost 300 experimental datasets of genome-wide nucleosome occupancy profiles determined in different cell types and more than 40 computational tools for the analysis of experimental nucleosome positioning data and prediction of intrinsic nucleosome formation probabilities from the DNA sequence. A manually curated, up to date list of these resources will be maintained at http://generegulation.info.
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Liu H, Zhang R, Xiong W, Guan J, Zhuang Z, Zhou S. A comparative evaluation on prediction methods of nucleosome positioning. Brief Bioinform 2013; 15:1014-27. [PMID: 24023366 DOI: 10.1093/bib/bbt062] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Nucleosome positioning plays an essential role in cellular processes by modulating accessibility of DNA to proteins. Many computational models have been developed to predict genome-wide nucleosome positions from DNA sequences. Comparative analysis of predicted and experimental nucleosome positioning maps facilitates understanding the regulatory mechanisms of transcription and DNA replication. Therefore, a comprehensive evaluation of existing computational methods is important and useful for biologists to choose appropriate ones in their research. In this article, we carried out a performance comparison among eight widely used computational methods on four species including yeast, fruitfly, mouse and human. In particular, we compared these methods on different regions of each species such as gene sequences, promoters and 5'UTR exons. The experimental results show that the performances of the two latest versions of the thermodynamic model are relatively steadier than the other four methods. Moreover, these methods are workable on four species, but their performances decrease gradually from yeast to human, indicating that the fundamental mechanism of nucleosome positioning is conserved through the evolution process, but more and more factors participate in the determination of nucleosome positions, which leads to sophisticated regulation mechanisms.
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Nikolaou C, Bermúdez I, Manichanh C, García-Martinez J, Guigó R, Pérez-Ortín JE, Roca J. Topoisomerase II regulates yeast genes with singular chromatin architectures. Nucleic Acids Res 2013; 41:9243-56. [PMID: 23935120 PMCID: PMC3814376 DOI: 10.1093/nar/gkt707] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Eukaryotic topoisomerase II (topo II) is the essential decatenase of newly replicated chromosomes and the main relaxase of nucleosomal DNA. Apart from these general tasks, topo II participates in more specialized functions. In mammals, topo IIα interacts with specific RNA polymerases and chromatin-remodeling complexes, whereas topo IIβ regulates developmental genes in conjunction with chromatin remodeling and heterochromatin transitions. Here we show that in budding yeast, topo II regulates the expression of specific gene subsets. To uncover this, we carried out a genomic transcription run-on shortly after the thermal inactivation of topo II. We identified a modest number of genes not involved in the general stress response but strictly dependent on topo II. These genes present distinctive functional and structural traits in comparison with the genome average. Yeast topo II is a positive regulator of genes with well-defined promoter architecture that associates to chromatin remodeling complexes; it is a negative regulator of genes extremely hypo-acetylated with complex promoters and undefined nucleosome positioning, many of which are involved in polyamine transport. These findings indicate that yeast topo II operates on singular chromatin architectures to activate or repress DNA transcription and that this activity produces functional responses to ensure chromatin stability.
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Affiliation(s)
- Christoforos Nikolaou
- Molecular Biology Institute of Barcelona, CSIC, 08028 Barcelona, Spain, Department of Biology, University of Crete, 71409 Heraklion, Greece, Department of Genetics and ERI Biotecmed, University of Valencia, 46100 Burjassot, Spain, Centre for Genomic Regulation (CRG), 08003 Barcelona, Spain and Department of Biochemistry and Molecular Biology and ERI Biotecmed, University of Valencia, 46100 Burjassot, Spain
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DNA-methylation effect on cotranscriptional splicing is dependent on GC architecture of the exon-intron structure. Genome Res 2013; 23:789-99. [PMID: 23502848 PMCID: PMC3638135 DOI: 10.1101/gr.143503.112] [Citation(s) in RCA: 164] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
DNA methylation is known to regulate transcription and was recently found to be involved in exon recognition via cotranscriptional splicing. We recently observed that exon–intron architectures can be grouped into two classes: one with higher GC content in exons compared to the flanking introns, and the other with similar GC content in exons and introns. The first group has higher nucleosome occupancy on exons than introns, whereas the second group exhibits weak nucleosome marking of exons, suggesting another type of epigenetic marker distinguishes exons from introns when GC content is similar. We find different and specific patterns of DNA methylation in each of the GC architectures; yet in both groups, DNA methylation clearly marks the exons. Exons of the leveled GC architecture exhibit a significantly stronger DNA methylation signal in relation to their flanking introns compared to exons of the differential GC architecture. This is accentuated by a reduction of the DNA methylation level in the intronic sequences in proximity to the splice sites and shows that different epigenetic modifications mark the location of exons already at the DNA level. Also, lower levels of methylated CpGs on alternative exons can successfully distinguish alternative exons from constitutive ones. Three positions at the splice sites show high CpG abundance and accompany elevated nucleosome occupancy in a leveled GC architecture. Overall, these results suggest that DNA methylation affects exon recognition and is influenced by the GC architecture of the exon and flanking introns.
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Moleirinho A, Seixas S, Lopes AM, Bento C, Prata MJ, Amorim A. Evolutionary constraints in the β-globin cluster: the signature of purifying selection at the δ-globin (HBD) locus and its role in developmental gene regulation. Genome Biol Evol 2013; 5:559-71. [PMID: 23431002 PMCID: PMC3622298 DOI: 10.1093/gbe/evt029] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/16/2013] [Indexed: 12/15/2022] Open
Abstract
Human hemoglobins, the oxygen carriers in the blood, are composed by two α-like and two β-like globin monomers. The β-globin gene cluster located at 11p15.5 comprises one pseudogene and five genes whose expression undergoes two critical switches: the embryonic-to-fetal and fetal-to-adult transition. HBD encodes the δ-globin chain of the minor adult hemoglobin (HbA2), which is assumed to be physiologically irrelevant. Paradoxically, reduced diversity levels have been reported for this gene. In this study, we sought a detailed portrait of the genetic variation within the β-globin cluster in a large human population panel from different geographic backgrounds. We resequenced the coding and noncoding regions of the two adult β-globin genes (HBD and HBB) in European and African populations, and analyzed the data from the β-globin cluster (HBE, HBG2, HBG1, HBBP1, HBD, and HBB) in 1,092 individuals representing 14 populations sequenced as part of the 1000 Genomes Project. Additionally, we assessed the diversity levels in nonhuman primates using chimpanzee sequence data provided by the PanMap Project. Comprehensive analyses, based on classic neutrality tests, empirical and haplotype-based studies, revealed that HBD and its neighbor pseudogene HBBP1 have mainly evolved under purifying selection, suggesting that their roles are essential and nonredundant. Moreover, in the light of recent studies on the chromatin conformation of the β-globin cluster, we present evidence sustaining that the strong functional constraints underlying the decreased contemporary diversity at these two regions were not driven by protein function but instead are likely due to a regulatory role in ontogenic switches of gene expression.
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Affiliation(s)
- Ana Moleirinho
- Institute of Molecular Pathology and Immunology of University of Porto (IPATIMUP), Porto, Portugal.
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Babbitt GA, Schulze KV. Codons support the maintenance of intrinsic DNA polymer flexibility over evolutionary timescales. Genome Biol Evol 2012; 4:954-65. [PMID: 22936074 PMCID: PMC3468960 DOI: 10.1093/gbe/evs073] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/21/2012] [Indexed: 01/02/2023] Open
Abstract
Despite our long familiarity with how the genetic code specifies the amino acid sequence, we still know little about why it is organized in the way that it is. Contrary to the view that the organization of the genetic code is a "frozen accident" of evolution, recent studies have demonstrated that it is highly nonrandom, with implications for both codon assignment and usage. We hypothesize that this inherent nonrandomness may facilitate the coexistence of both sequence and structural information in DNA. Here, we take advantage of a simple metric of intrinsic DNA flexibility to analyze mutational effects on the four phosphate linkages present in any given codon. Application of a simple evolutionary neutral model of substitution to random sequences, translated with alternative genetic codes, reveals that the standard code is highly optimized to favor synonymous substitutions that maximize DNA polymer flexibility, potentially counteracting neutral evolutionary drift toward stiffer DNA caused by spontaneous deamination. Comparison to existing mutational patterns in yeast also demonstrates evidence of strong selective constraint on DNA flexibility, especially at so-called "silent" sites. We also report a fundamental relationship between DNA flexibility, codon usage bias, and several important evolutionary descriptors of comparative genomics (e.g., base composition, transition/transversion ratio, and nonsynonymous vs. synonymous substitution rate). Recent advances in structural genomics have emphasized the role of the DNA polymer's flexibility in both gene function and whole genome folding, thereby implicating possible reasons for codons to facilitate the multiplexing of both genetic and structural information within the same molecular context.
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Affiliation(s)
- G A Babbitt
- TH Gosnell School of Life Sciences, Rochester Institute of Technology, Rochester, NY, USA.
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Nucleosome positioning in a model of active chromatin remodeling enzymes. Proc Natl Acad Sci U S A 2011; 108:7799-803. [PMID: 21518900 DOI: 10.1073/pnas.1015206108] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Accounting for enzyme-mediated active sliding, disassembly, and sequence-dependent positioning of nucleosomes, we simulate nucleosome occupancy over cell-cycle-scale times using a stochastic kinetic model. We show that ATP-dependent active nucleosome sliding and nucleosome removal processes are essential to obtain in vivo-like nucleosome positioning. While active sliding leads to dense nucleosome filling, sliding events alone cannot ensure sequence-dependent nucleosome positioning: Active nucleosome removal is the crucial remodeling event that drives positioning. We also show that remodeling activity changes nucleosome dynamics from glassy to liquid-like, and that remodeling dramatically influences exposure dynamics of promoter regions.
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