title: Gene silencing: trans-histone regulatory pathway in chromatin.
abstract: The fundamental unit of eukaryotic chromatin, the nucleosome, consists of genomic DNA wrapped around the conserved histone proteins H3, H2B, H2A and H4, all of which are variously modified at their amino- and carboxy-terminal tails to influence the dynamics of chromatin structure and function -- for example, conjugation of histone H2B with ubiquitin controls the outcome of methylation at a specific lysine residue (Lys 4) on histone H3, which regulates gene silencing in the yeast Saccharomyces cerevisiae. Here we show that ubiquitination of H2B is also necessary for the methylation of Lys 79 in H3, the only modification known to occur away from the histone tails, but that not all methylated lysines in H3 are regulated by this 'trans-histone' pathway because the methylation of Lys 36 in H3 is unaffected. Given that gene silencing is regulated by the methylation of Lys 4 and Lys 79 in histone H3, we suggest that H2B ubiquitination acts as a master switch that controls the site-selective histone methylation patterns responsible for this silencing.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia Health System, Charlottesville, Virginia 22908, USA.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Briggs
authors.forename: Tiaojiang
authors.initials: T
authors.lastname: Xiao
authors.forename: Zu-Wen
authors.initials: ZW
authors.lastname: Sun
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Caldwell
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Shabanowitz
authors.forename: Donald F
authors.initials: DF
authors.lastname: Hunt
authors.forename: C David
authors.initials: CD
authors.lastname: Allis
authors.forename: Brian D
authors.initials: BD
authors.lastname: Strahl
mesh_terms: D002843:Chromatin / Q000737:chemistry / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D020868:Gene Silencing; D011495:Histone-Lysine N-Methyltransferase; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D008025:Ligases / Q000378:metabolism; D008745:Methylation; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes
chemical_list: D002843:Chromatin; D006657:Histones; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C416235:Dot1 protein, S cerevisiae; D011495:Histone-Lysine N-Methyltransferase; D044763:Ubiquitin-Conjugating Enzymes; D008025:Ligases