Chromatin Remodeling and Transcription Repression

描述（由申请人提供）：atp依赖性染色质重塑参与转录，DNA复制，重组和DNA修复的调控。通常，这种染色质重塑与使DNA更容易接近其他DNA结合因子有关，从而促进它们与特定目标位点的结合。一类依赖atp的染色质重塑复合体，被称为模仿开关（ISWI）家族，具有全局调节染色质结构、形成抑制性染色质结构和参与转录抑制的一般特性。在酿酒酵母中有两个ISWl样基因，即ISW1和ISW2。Isw1p蛋白被组装成两个不同的复合物，称为ISW1a和ISW1b；而只发现了一个ISW2复合体。ISW2已被证明是减数分裂基因抑制所必需的，并被Ume6抑制蛋白招募。ISW1a/b最近也被证明参与转录终止。目前尚不清楚这些复合体如何重塑核小体，以及染色质中的净结构变化是什么。我们的实验室和Peter Becker的研究结果表明，ISWI重塑不会改变典型核小体结构，但也很清楚，这些结构确实促进了更凝聚的染色质纤维结构的形成。我们的建议是确定ISW2和ISW1如何与核小体结合，参与重塑的结构中间体是什么，以及这些变化如何影响染色质的高阶结构。

DESCRIPTION (provided by applicant): ATP-dependent chromatin remodeling is involved in the regulation of transcription, DNA replication, recombination, and DNA repair. Often this kind of chromatin remodeling is associated with making the DNA more accessible to other DNA-binding factors thereby promoting their binding to specific target sites. One class of ATP-dependent chromatin remodeling complexes, referred to as imitation switch (ISWI) family, has the general properties of globally regulating chromatin structure, forming repressive chromatin structures, and of being involved in transcription repression. In Saccharomyces cerevisiae there are two ISWl like genes, namely ISW1 and ISW2. The Isw1p protein is assembled into two distinct complexes referred to as ISW1a and ISW1b; whereas only one complex of ISW2 is found. ISW2 has been shown to be required for repression of meiotic genes and to be recruited by the Ume6 repressor protein. ISW1a/b have also been recently shown to be involved in transcription termination. It is not clear yet how these complexes remodel nucleosomes and what the net structural changes caused in chromatin. Results from our lab and those of Peter Becker have shown that ISWI remodeling does not change the canonical nucleosome structure and yet it is also clear that these do promote the formation of a more condensed chromatin fiber structure. Our proposal is to determine how ISW2 and ISW1 bind to nucleosomes, what are the structural intermediates involved in remodeling, and how do these changes affect the higher ordered structure of chromatin.