Schnell R, D'Ari L, Foss M, Goodman D, Rine J
Department of Biochemistry, University of California, Berkeley 94720.
Genetics. 1989 May;122(1):29-46. doi: 10.1093/genetics/122.1.29.
In order to learn more about other proteins that may be involved in repression of HML and HMR in Saccharomyces cerevisiae, extragenic suppressor mutations were identified that could restore repression in cells defective in SIR4, a gene required for function of the silencer elements flanking HML and HMR. These suppressor mutations, which define at least three new genes, SAN1, SAN2 and SAN3, arose at the frequency expected for loss-of-function mutations following mutagenesis. All san mutations were recessive. Suppression by san1 was allele-nonspecific, since san1 could suppress two very different alleles of SIR4, and was locus-specific since san1 was unable to suppress a SIR3 mutation or a variety of mutations conferring auxotrophies. The SAN1 gene was cloned, sequenced, and used to construct a null allele. The null allele had the same phenotype as the EMS-induced mutations and exhibited no pleiotropies of its own. Thus, the SAN1 gene was not essential. SAN1-mediated suppression was neither due to compensatory mutations in interacting proteins, nor to translational missense suppression. SAN1 may act posttranslationally to control the stability or activity of the SIR4 protein.
为了更多地了解酿酒酵母中可能参与HML和HMR基因沉默的其他蛋白质，我们鉴定了一些基因外抑制突变，这些突变可以在SIR4基因缺陷的细胞中恢复基因沉默，SIR4基因是HML和HMR两侧沉默子元件功能所必需的基因。这些抑制突变定义了至少三个新基因，即SAN1、SAN2和SAN3，它们的出现频率符合诱变后功能丧失突变的预期频率。所有san突变均为隐性突变。san1的抑制作用是非等位基因特异性的，因为san1可以抑制SIR4的两个非常不同的等位基因，并且是位点特异性的，因为san1无法抑制SIR3突变或多种导致营养缺陷型的突变。克隆、测序了SAN1基因，并用于构建一个无效等位基因。该无效等位基因具有与EMS诱导突变相同的表型，且自身无多效性。因此，SAN1基因不是必需的。SAN1介导的抑制作用既不是由于相互作用蛋白中的补偿性突变，也不是由于翻译错义抑制。SAN1可能在翻译后发挥作用，以控制SIR4蛋白的稳定性或活性。
