Johnson L M, Kayne P S, Kahn E S, Grunstein M
Molecular Biology Institute, University of California, Los Angeles 90024.
Proc Natl Acad Sci U S A. 1990 Aug;87(16):6286-90. doi: 10.1073/pnas.87.16.6286.
Repression of transcription from the silent mating loci (HML alpha and HMRa) is essential for mating ability in Saccharomyces cerevisiae. This silencing is known to require at least five proteins (SIR1, SIR2, SIR3, SIR4, and histone H4) and is accompanied by a change in chromatin structure. We show here that four positions of histone H4 (N-terminal residues 16, 17, 18, and 19) are crucial to silencing. HML alpha and HMRa are efficiently repressed when these positions are occupied by basic amino acids but are derepressed when substituted with glycine. These results suggest that acetylation of Lys-16 would lead to derepression of the silent mating loci. Three strong extragenic suppressors of the latter H4 mutations were isolated and determined to be located in SIR3. These suppressors allow high mating efficiencies in cells expressing either wild-type H4 or H4 containing single amino acid substitutions. They did not allow efficient mating in a strain that contained an H4 N-terminal deletion. These results indicate that the SIR3 mutations do not bypass the requirement for the H4 N terminus but, rather, allow repression in the presence of a less than optimal H4 N terminus. This provides a link between one of the SIR proteins and a component of chromatin.
沉默交配位点（HMLα和HMRa）的转录抑制对于酿酒酵母的交配能力至关重要。已知这种沉默至少需要五种蛋白质（SIR1、SIR2、SIR3、SIR4和组蛋白H4），并且伴随着染色质结构的变化。我们在此表明，组蛋白H4的四个位置（N端残基16、17、18和19）对沉默至关重要。当这些位置被碱性氨基酸占据时，HMLα和HMRa被有效抑制，但当被甘氨酸取代时则被解除抑制。这些结果表明，赖氨酸-16的乙酰化会导致沉默交配位点的去抑制。分离出了后一种H4突变的三个强基因外抑制子，并确定它们位于SIR3中。这些抑制子在表达野生型H4或含有单个氨基酸取代的H4的细胞中允许高交配效率。它们在含有H4 N端缺失的菌株中不允许有效交配。这些结果表明，SIR3突变不会绕过对H4 N端的需求，而是在存在次优H4 N端的情况下允许抑制。这提供了一种SIR蛋白与染色质成分之间的联系。
