Ivy J M, Klar A J, Hicks J B
Mol Cell Biol. 1986 Feb;6(2):688-702. doi: 10.1128/mcb.6.2.688-702.1986.
Mating type in the yeast Saccharomyces cerevisiae is determined by the MAT (a or alpha) locus. HML and HMR, which usually contain copies of alpha and a mating type information, respectively, serve as donors in mating type interconversion and are under negative transcriptional control. Four trans-acting SIR (silent information regulator) loci are required for repression of transcription. A defect in any SIR gene results in expression of both HML and HMR. The four SIR genes were isolated from a genomic library by complementation of sir mutations in vivo. DNA blot analysis suggests that the four SIR genes share no sequence homology. RNA blots indicate that SIR2, SIR3, and SIR4 each encode one transcript and that SIR1 encodes two transcripts. Null mutations, made by replacement of the normal genomic allele with deletion-insertion mutations created in the cloned SIR genes, have a Sir- phenotype and are viable. Using the cloned genes, we showed that SIR3 at a high copy number is able to suppress mutations of SIR4. RNA blot analysis suggests that this suppression is not due to transcriptional regulation of SIR3 by SIR4; nor does any SIR4 gene transcriptionally regulate another SIR gene. Interestingly, a truncated SIR4 gene disrupts regulation of the silent mating type loci. We propose that interaction of at least the SIR3 and SIR4 gene products is involved in regulation of the silent mating type genes.
酿酒酵母中的交配型由MAT（a或α）基因座决定。HML和HMR通常分别包含α和a交配型信息的拷贝，在交配型相互转换中作为供体，并且处于负转录调控之下。转录抑制需要四个反式作用的SIR（沉默信息调节因子）基因座。任何一个SIR基因的缺陷都会导致HML和HMR的表达。通过体内sir突变的互补作用从基因组文库中分离出四个SIR基因。DNA印迹分析表明这四个SIR基因没有序列同源性。RNA印迹表明SIR2、SIR3和SIR4各自编码一种转录本，而SIR1编码两种转录本。通过用在克隆的SIR基因中产生的缺失插入突变替换正常基因组等位基因产生的无效突变具有Sir-表型且是可行的。利用克隆的基因，我们表明高拷贝数的SIR3能够抑制SIR4的突变。RNA印迹分析表明这种抑制不是由于SIR4对SIR3的转录调控；任何SIR4基因也不会转录调控另一个SIR基因。有趣的是，一个截短的SIR4基因破坏了沉默交配型基因座的调控。我们提出至少SIR3和SIR4基因产物的相互作用参与了沉默交配型基因的调控。
