Conditional silencing: the HMRE mating-type silencer exerts a rapidly reversible position effect on the yeast HSP82 heat shock gene.
Conditional silencing: the HMRE mating-type silencer exerts a rapidly reversible position effect on the yeast HSP82 heat shock gene.
复制标题
条件沉默：HMRE交配型沉默子对酵母HSP82热休克基因产生快速可逆的位置效应。
DOI：
10.1128/mcb.13.2.727-738.1993
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发表时间：
1993
影响因子：
5.3
通讯作者：
Gross,DS
中科院分区：
文献类型：
--
作者：
Lee,S;Gross,DS
TheHMREsilencer ofSaccharomyces cerevisiaehas been previously shown to transcriptionally repress class II and class III genes integrated within theHMRsilent mating-type locus up to 2.6 kb away. Here we study the ability of this element to repress at an ectopic position, independent of sequences normally associated with it. When integrated 750 bp upstream of theHSP82heat shock gene, the silencer represses basal-level transcription ~ 5-fold but has no effect on chemical- or heat-shock-induced expression. Such conditional silencing is also seen when theHMRE/HSP82allele is carried on a centromeric episome or when the entireHMRadomain is transplaced 2.7 kb upstream ofHSP82. Notably, the a1 promoter within the immigrantHMRalocus remains fully repressed at the same timeHSP82is derepressed. The position effect mediated by theEsilencer is absolutely dependent on the presence of a functionalSIR4gene product, is lost within 1 min following stress induction, and is fully reestablished within 15 min following a return to nonstressful conditions. Similar kinetics of reestablishment are seen inHMRE/HSP82andHMRa/HSP82strains, indicating that complete repression can be mediated over thousands of base pairs within minutes. DNase I chromatin mapping reveals that the ABF1, RAP1, and autonomously replicating sequence factor binding sites within the silencer are constitutively occupied in chromatin, unaltered by heat shock or the presence ofSIR4. Similarly, the heat shock factor binding site upstream ofHSP82remains occupied under such conditions, suggesting concurrent occupancy of silencer and activator binding sites. Our results are consistent with a model in which silencing at theHMRE/HSP82allele is mediated by direct or indirect contacts between the silencer protein complex and heat shock factor.
