New alleles of SIR2 define cell-cycle-specific silencing functions.
The establishment of transcriptional silencing in yeast requires cell-cycle progression, but the nature of this requirement is unknown. Sir2 is a protein deacetylase that is required for gene silencing in yeast. We have used temperature-sensitive alleles of the SIR2 gene to assess Sir2's contribution to silencing as a function of the cell cycle. When examined in vivo, these conditional alleles fall into two classes: one class exhibits a loss of silencing when raised to the nonpermissive temperature regardless of cell-cycle position, while the second class exhibits a mitosis-specific silencing defect. Alleles of the first class have a primary defect in protein deacetylase activity, while the alleles of the second class are specifically defective in Sir2-Sir4 interactions at nonpermissive temperatures. Using a SIR2 temperature-sensitive allele, we show that silencing can be established at the HML locus during progression through the G2/M-G1 interval. These results suggest that yeast heterochromatin undergoes structural transitions as a function of the cell cycle and support the existence of a critical assembly step for silent chromatin in mitosis.
Matecic
Mirela
M
Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT 06459, USA.
Martins-Taylor
Kristen
K
Hickman
Merrit
M
Tanny
Jason
J
Moazed
Danesh
D
Holmes
Scott G
SG
D000483:Alleles; D042002:Chromatin Assembly and Disassembly / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal / Q000235:genetics*; D020868:Gene Silencing; D006655:Histone Deacetylases / Q000235:genetics* / Q000378:metabolism; D006358:Hot Temperature; D008938:Mitosis / Q000235:genetics; D040641:Quantitative Trait Loci / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics* / Q000254:growth & development; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D056565:Sirtuin 2; D037761:Sirtuins / Q000235:genetics* / Q000378:metabolism
C061573:SIR4 protein, S cerevisiae; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases