title: Widespread remodeling of mid-coding sequence nucleosomes by Isw1.
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, mid-coding 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.
authors.affiliation: Department of Molecular genetics, Weizmann Institute of Science, Herzl street, Rehovot 76100, Israel. itay.tirosh@weizmann.ac.il
authors.forename: Itay
authors.initials: I
authors.lastname: Tirosh
authors.forename: Nadejda
authors.initials: N
authors.lastname: Sigal
authors.forename: Naama
authors.initials: N
authors.lastname: Barkai
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D042002:Chromatin Assembly and Disassembly / Q000235:genetics*; D045584:Chromosome Positioning / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D006657:Histones / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D008745:Methylation; D008957:Models, Genetic; D009707:Nucleosomes / Q000235:genetics*; D016366:Open Reading Frames / Q000235:genetics*; D012319:RNA Polymerase II / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity; D024363:Transcription Initiation Site
chemical_list: D004268:DNA-Binding Proteins; D006657:Histones; D009707:Nucleosomes; D029701:Saccharomyces cerevisiae Proteins; D012319:RNA Polymerase II; D000251:Adenosine Triphosphatases; C470546:ISW1 protein, S cerevisiae; D008239:Lysine
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