Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: Widespread remodeling of mid-coding sequence nucleosomes by Isw1. | Tirosh et al. Genome Biology 2010 11 R49 http 2010 11 5 R49 w Genome Biology RESEARCH _ Open Access Widespread remodeling of mid-eoding sequence nucleosomes by Isw1 ItayTirosh 1 Nadejda Sigal1 2 and Naama Barkai1 Abstract Background The positions of nucleosomes along eukaryotic DNA are defined by the local DNA sequence and are further tuned by the activity of chromatin remodelers. While the genome-wide effect of most remodelers has not been described recent studies in Saccharomyces cerevisiae have shown that Isw2 prevents ectopic expression of anti-sense and suppressed transcripts at gene ends. Results We examined the genome-wide function of the Isw2 homologue Isw1 by mapping nucleosome positioning in S. cerevisiae and Saccharomyces paradoxus strains deleted of ISW1. We found that Isw1 functions primarily within coding regions of genes consistent with its putative role in transcription elongation. Upon deletion of ISW1 midcoding nucleosomes were shifted upstream towards the 5 ends in about half of the genes. Isw1-dependent shifts were correlated with trimethylation of H3K79 and were enriched at genes with internal cryptic initiation sites. Conclusions Our results suggest a division of labor between Isw1 and Isw2 whereby Isw2 maintains repressive chromatin structure at gene ends while Isw1 has a similar function at mid-coding regions. The differential specificity of the two remodelers may be specified through interactions with particular histone marks. Background Chromatin is composed of core nucleosome particles each containing approximately 147 bp of double-stranded DNA wrapped around a histone octamer 1 . Nucleosomes restrict the accessibility of proteins to the DNA thereby influencing DNA transcription replication recombination and repair 2-4 . Nucleosome positioning is determined to a large extent by the local DNA sequence and its affinity to nucleosomes 5-7 but is also dynamically altered by the activity of a large number of .
