Saccharomyces cerevisiaeLinker Histone Hho1p Functionally Interacts with Core Histone H4 and Negatively Regulates the Establishment of Transcriptionally Silent Chromatin

ABSTRACT Silent chromatin in Saccharomyces cerevisiae is established in a stepwise process involving the SIR complex, comprised of the histone deacetylase Sir2 and the structural components Sir3 and Sir4. The Sir3 protein, which is the primary histone-binding component of the SIR complex, forms oligomers in vitro and has been proposed to mediate the spreading of the SIR complex along the chromatin fiber. In order to analyze the role of Sir3 in the spreading of the SIR complex, we performed a targeted genetic screen for alleles of SIR3 that dominantly disrupt silencing. Most mutations mapped to a single surface in the conserved N-terminal BAH domain, while one, L738P, localized to the AAA ATPase-like domain within the C-terminal half of Sir3. The BAH point mutants, but not the L738P mutant, disrupted the interaction between Sir3 and nucleosomes. In contrast, Sir3-L738P bound the N-terminal tail of histone H4 more strongly than wild-type Sir3, indicating that misregulation of the Sir3 C-terminal histone-binding activity also disrupted spreading. Our results underscore the importance of proper interactions between Sir3 and the nucleosome in silent chromatin assembly. We propose a model for the spreading of the SIR complex along the chromatin fiber through the two distinct histone-binding domains in Sir3.

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PR-Set7 Is a Nucleosome-Specific Methyltransferase that Modifies Lysine 20 of Histone H4 and Is Associated with Silent Chromatin

Molecular Cell ◽

10.1016/s1097-2765(02)00548-8 ◽

2002 ◽

Vol 9 (6) ◽

pp. 1201-1213 ◽

Cited By ~ 363

Author(s):

Kenichi Nishioka ◽

Judd C. Rice ◽

Kavitha Sarma ◽

Hediye Erdjument-Bromage ◽

Janis Werner ◽

...

Keyword(s):

Silent Chromatin ◽

Histone H4

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Core Histones and HIRIP3, a Novel Histone-Binding Protein, Directly Interact with WD Repeat Protein HIRA

Molecular and Cellular Biology ◽

10.1128/mcb.18.9.5546 ◽

1998 ◽

Vol 18 (9) ◽

pp. 5546-5556 ◽

Cited By ~ 59

Author(s):

Stéphanie Lorain ◽

Jean-Pierre Quivy ◽

Frédérique Monier-Gavelle ◽

Christine Scamps ◽

Yann Lécluse ◽

...

Keyword(s):

Protein Interaction ◽

Developmental Disorders ◽

Core Histone ◽

Histone H4 ◽

Interacting Protein ◽

Amino Terminal ◽

Core Histones ◽

Α Helix ◽

Interaction Trap

ABSTRACT The human HIRA gene has been named after Hir1p and Hir2p, two corepressors which together appear to act on chromatin structure to control gene transcription in Saccharomyces cerevisiae. HIRA homologs are expressed in a regulated fashion during mouse and chicken embryogenesis, and the human gene is a major candidate for the DiGeorge syndrome and related developmental disorders caused by a reduction to single dose of a fragment of chromosome 22q. Western blot analysis and double-immunofluorescence experiments using a specific antiserum revealed a primary nuclear localization of HIRA. Similar to Hir1p, HIRA contains seven amino-terminal WD repeats and probably functions as part of a multiprotein complex. HIRA and core histone H2B were found to physically interact in a yeast double-hybrid protein interaction trap, in GST pull-down assays, and in coimmunoprecipitation experiments performed from cellular extracts. In vitro, HIRA also interacted with core histone H4. H2B- and H4-binding domains were overlapping but distinguishable in the carboxy-terminal region of HIRA, and the region for HIRA interaction was mapped to the amino-terminal tail of H2B and the second α helix of H4. HIRIP3 (HIRA-interacting protein 3) is a novel gene product that was identified from its HIRA-binding properties in the yeast protein interaction trap. In vitro, HIRIP3 directly interacted with HIRA but also with core histones H2B and H3, suggesting that a HIRA-HIRIP3-containing complex could function in some aspects of chromatin and histone metabolism. Insufficient production of HIRA, which we report elsewhere interacts with homeodomain-containing DNA-binding factors during mammalian embryogenesis, could perturb the stoichiometric assembly of multimolecular complexes required for normal embryonic development.

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Mutations in the Nucleosome Core Enhance Transcriptional Silencing

Molecular and Cellular Biology ◽

10.1128/mcb.25.5.1846-1859.2005 ◽

2005 ◽

Vol 25 (5) ◽

pp. 1846-1859 ◽

Cited By ~ 18

Author(s):

Eugenia Y. Xu ◽

Xin Bi ◽

Michael J. Holland ◽

Daniel E. Gottschling ◽

James R. Broach

Keyword(s):

Transcriptional Silencing ◽

Silent Chromatin ◽

Histone H4 ◽

Core Domain ◽

Nucleosome Core ◽

The Core ◽

Sir Proteins ◽

Rate Of Decay ◽

Silent State ◽

Subtelomeric Regions

ABSTRACT Transcriptional silencing in Saccharomyces requires specific nucleosome modifications promoted in part by a complex of Sir proteins that binds to the modified nucleosomes. Recent evidence suggests that modifications of both the histone amino termini and the core domain of nucleosomes contribute to silencing. We previously identified histone H4 mutations affecting residues in the core of the nucleosome that yield enhanced silencing at telomeres. Here we show that enhanced silencing induced by these mutations increases the proportion of cells in which telomeres and silent mating-type loci are in the silent state. One H4 mutation affects the expression of a subset of genes whose expression is altered by deletion of HTZ1, which encodes the histone variant H2A.Z, suggesting that the mutation may antagonize H2A.Z incorporation into nucleosomes. A second mutation causes the spread of silencing into subtelomeric regions that are not normally silenced in wild-type cells. Mechanistically, this mutation does not significantly accelerate the formation of silent chromatin but, rather, reduces the rate of decay of the silenced state. We propose that these mutations use distinct mechanisms to affect the dynamic interplay between activation and repression at the boundary between active and silent chromatin.

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