Chromatin Remodeling and Transcription Repression

描述（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修复的调节。通常这种染色质重塑与使DNA更容易接近其他DNA结合因子，从而促进它们与特定靶位点的结合有关。一类ATP依赖的染色质重塑复合物，称为模仿开关（imitation switch，ISWI）家族，具有全局调节染色质结构、形成抑制性染色质结构以及参与转录抑制的一般性质。在酿酒酵母中，存在两个ISWl样基因，即ISWl和ISW 2。Isw 1 p蛋白被组装成两个不同的复合物，称为ISW 1a和ISW 1b，而只有一个复合物ISW 2被发现。ISW 2已被证明是减数分裂基因的阻遏所需的，并被Ume 6阻遏蛋白招募。ISW 1a/B最近也被证明参与转录终止。目前尚不清楚这些复合物如何重塑核小体以及在染色质中引起的净结构变化。我们实验室和Peter Becker实验室的结果表明，ISWI重塑不会改变典型的核小体结构，但也很明显，这些确实促进了更浓缩的染色质纤维结构的形成。我们的建议是确定ISW 2和ISW 1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级结构。

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.