Moreira J M, Holmberg S
Department of Genetics, Institute of Molecular Biology, University of Copenhagen, Oster Farimagsgade 2A, DK-1353 Copenhagen K, Denmark.
EMBO J. 1999 May 17;18(10):2836-44. doi: 10.1093/emboj/18.10.2836.
In eukaryotes, DNA is packaged into chromatin, a compact structure that must be disrupted when genes are transcribed by RNA polymerase II. For transcription to take place, chromatin is remodeled via nucleosome disruption or displacement, a fundamental transcriptional regulatory mechanism in eukaryotic organisms. Here we show that the yeast chromatin-remodeling complex, RSC (remodels the structure of chromatin), isolated on the basis of homology to the SWI/SNF complex, is required for proper transcriptional regulation and nucleosome positioning in the highly inducible CHA1 promoter. In the absence of Sth1p/Nps1p (a homolog of Swi2p/Snf2p) or of Swh3p (a homolog of Swi3p), expression of CHA1 in non-induced cells is increased to a level comparable with that of fully induced cells. Furthermore, in non-induced cells depleted for Sth1p/Nps1p or Swh3p, a nucleosome positioned over the TATA box of the CHA1 promoter is disrupted, an architectural change normally only observed during transcriptional induction. In addition, deletion of the gene-specific activator Cha4p did not affect derepression of CHA1 in cells depleted for Swh3p. Thus, CHA1 constitutes a target for the RSC complex, and we propose that RSC is essential for maintaining a repressive chromatin structure at the CHA1 promoter.
在真核生物中，DNA被包装成染色质，这是一种紧密的结构，当基因由RNA聚合酶II转录时必须被破坏。为了进行转录，染色质通过核小体的破坏或移位进行重塑，这是真核生物中一种基本的转录调控机制。在这里，我们表明，基于与SWI/SNF复合物的同源性分离出的酵母染色质重塑复合物RSC（重塑染色质结构），对于高度可诱导的CHA1启动子中的适当转录调控和核小体定位是必需的。在没有Sth1p/Nps1p（Swi2p/Snf2p的同源物）或Swh3p（Swi3p的同源物）的情况下，非诱导细胞中CHA1的表达增加到与完全诱导细胞相当的水平。此外，在耗尽Sth1p/Nps1p或Swh3p的非诱导细胞中，位于CHA1启动子TATA框上的核小体被破坏，这种结构变化通常只在转录诱导过程中观察到。此外，基因特异性激活剂Cha4p的缺失并不影响耗尽Swh3p的细胞中CHA1的去抑制。因此，CHA1构成了RSC复合物的一个靶点，我们提出RSC对于在CHA1启动子处维持抑制性染色质结构至关重要。
