title: The Mi-2 homolog Mit1 actively positions nucleosomes within heterochromatin to suppress transcription.
abstract: Mit1 is the putative chromatin remodeling subunit of the fission yeast Snf2/histone deacetylase (HDAC) repressor complex (SHREC) and is known to repress transcription at regions of heterochromatin. However, how Mit1 modifies chromatin to silence transcription is largely unknown. Here we report that Mit1 mobilizes histone octamers in vitro and requires ATP hydrolysis and conserved chromatin tethering domains, including a previously unrecognized chromodomain, to remodel nucleosomes and silence transcription. Loss of Mit1 remodeling activity results in nucleosome depletion at specific DNA sequences that display low intrinsic affinity for the histone octamer, but its contribution to antagonizing RNA polymerase II (Pol II) access and transcription is not restricted to these sites. Genetic epistasis analyses demonstrate that SHREC subunits and the transcription-coupled Set2 histone methyltransferase, which is involved in suppression of cryptic transcription at actively transcribed regions, cooperate to silence heterochromatic transcripts. In addition, we have demonstrated that Mit1's remodeling activity contributes to SHREC function independently of Clr3's histone deacetylase activity on histone H3 K14. We propose that Mit1 is a chromatin remodeling factor that cooperates with the Clr3 histone deacetylase of SHREC and other chromatin modifiers to stabilize heterochromatin structure and to prevent access to the transcriptional machinery.
authors.affiliation: Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee, USA.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Creamer
authors.forename: Godwin
authors.initials: G
authors.lastname: Job
authors.forename: Sreenath
authors.initials: S
authors.lastname: Shanker
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Neale
authors.forename: Yuan-chi
authors.initials: YC
authors.lastname: Lin
authors.forename: Blaine
authors.initials: B
authors.lastname: Bartholomew
authors.forename: Janet F
authors.initials: JF
authors.lastname: Partridge
mesh_terms: D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000235:genetics; D042002:Chromatin Assembly and Disassembly / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal; D006570:Heterochromatin / Q000235:genetics*; D011495:Histone-Lysine N-Methyltransferase / Q000235:genetics; D006657:Histones / Q000235:genetics / Q000378:metabolism; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009707:Nucleosomes / Q000235:genetics*; D034622:RNA Interference; D012319:RNA Polymerase II / Q000037:antagonists & inhibitors; D034741:RNA, Small Interfering; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000235:genetics* / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D018797:Cell Cycle Proteins; C115302:Clr3 protein, S pombe; D006570:Heterochromatin; D006657:Histones; C000589388:Mit1 protein, S pombe; D009707:Nucleosomes; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D029702:Schizosaccharomyces pombe Proteins; D011495:Histone-Lysine N-Methyltransferase; C527202:Set2 protein, S pombe; D012319:RNA Polymerase II; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex