Shore D, Squire M, Nasmyth K A
EMBO J. 1984 Dec 1;3(12):2817-23. doi: 10.1002/j.1460-2075.1984.tb02214.x.
The mating type of haploid yeast (a or alpha) is determined by information present at the MAT locus. Identical copies of a and alpha information are present at distal loci (HMR and HML), but transcription of these copies is repressed by the action, in trans, of four unlinked genes called SIR (silent information regulator). Repression by SIR also requires, in cis, DNA sequences called E which are found to the left of HML and HMR (but not MAT) and are greater than 1 kb from the mating-type gene promoters. SIR control can act on other promoters when they are brought near the E sequence, and thus the SIR gene products act in some general manner to repress transcription. We have determined the DNA sequence of two fragments which complement mutations in the SIR2 and SIR3 genes and show that these contain the structural genes by mapping the cloned sequences onto the yeast chromosome. The SIR2 and SIR3 coding sequences were identified by constructing gene disruptions and using these mutations to replace the normal chromosomal copies. Such null mutants of both SIR2 and SIR3 are defective in the position-effect control of the silent loci but have no other detectable phenotype. We have mapped the 5' and 3' ends of the SIR2 and SIR3 mRNAs and show that their level is unaffected by mutations in any of the four known SIR complementation groups.
单倍体酵母的交配型（a或α）由MAT基因座处的信息决定。a和α信息的相同拷贝存在于远端基因座（HMR和HML），但这些拷贝的转录受到四个不连锁基因SIR（沉默信息调节因子）反式作用的抑制。SIR的抑制作用在顺式中还需要称为E的DNA序列，该序列位于HML和HMR（而非MAT）的左侧，且距离交配型基因启动子大于1 kb。当其他启动子靠近E序列时，SIR控制可作用于它们，因此SIR基因产物以某种一般方式抑制转录。我们确定了两个片段的DNA序列，它们可互补SIR2和SIR3基因中的突变，并通过将克隆序列定位到酵母染色体上表明这些片段包含结构基因。通过构建基因破坏并使用这些突变取代正常染色体拷贝来鉴定SIR2和SIR3编码序列。SIR2和SIR3的这种缺失突变体在沉默基因座的位置效应控制方面存在缺陷，但没有其他可检测到的表型。我们已定位SIR2和SIR3 mRNA的5'和3'末端，并表明它们的水平不受四个已知SIR互补组中任何一个突变的影响。
