Amino termini of histones H3 and H4 are required for a1-alpha2 repression in yeast

Mol Cell Biol. 1997 Nov;17(11):6555-62. doi: 10.1128/MCB.17.11.6555.

Abstract

The Saccharomyces cerevisiae alpha2 repressor controls two classes of cell-type-specific genes in yeast through association with different partners. alpha2-Mcm1 complexes repress a cell-specific gene expression in haploid alpha cells and diploid a/alpha cells, while a1-alpha2 complexes repress haploid-specific genes in diploid cells. In both cases, repression is mediated through Ssn6-Tu1 corepressor complexes that are recruited via direct interactions with alpha2. We have previously shown that nucleosomes are positioned adjacent to the alpha2-Mcm1 operator under conditions of repression and that Tupl interacts directly with histones H3 and H4. Here, we examine the role of chromatin in a1-alpha2 repression to determine if chromatin is a general feature of repression by Ssn6-Tup1. We find that mutations in the amino terminus of histone H4 cause a 4- to 11-fold derepression of a reporter gene under a1-alpha2 control, while truncation of the H3 amino terminus has a more modest (3-fold or less) effect. Strikingly, combination of the H3 truncation with an H4 mutation causes a 40-fold decrease in repression, clearly indicating a central role for these histones in a1-alpha2-mediated repression. However, in contrast to the ordered positioning of nucleosomes adjacent to the alpha2-Mcm1 operator, nucleosomes are not positioned adjacent to the a1-alpha2 operator in diploid cells. Our data indicate that chromatin is important to Ssn6-Tup1-mediated repression but that the degrees of chromatin organization directed by these proteins differ at different promoters.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Chromatin / metabolism*
  • DNA-Binding Proteins / metabolism
  • Fungal Proteins / metabolism
  • Gene Expression Regulation, Fungal*
  • Genes, Reporter
  • Histones / genetics
  • Histones / metabolism*
  • Homeodomain Proteins / metabolism
  • Models, Genetic
  • Nuclear Proteins*
  • Nucleosomes / metabolism
  • Operator Regions, Genetic
  • Ploidies
  • Promoter Regions, Genetic
  • Repressor Proteins / metabolism*
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae Proteins*

Substances

  • CYC8 protein, S cerevisiae
  • Chromatin
  • DNA-Binding Proteins
  • Fungal Proteins
  • Histones
  • Homeodomain Proteins
  • MATA2 protein, S cerevisiae
  • Nuclear Proteins
  • Nucleosomes
  • Repressor Proteins
  • Saccharomyces cerevisiae Proteins
  • TUP1 protein, S cerevisiae