Eukaryotic Chromatin Structure and Gene Regulation

我们小组继续研究染色质结构和真核基因表达的调控。今年，我们在了解小鼠核小体重塑因子(NURF)依赖三磷酸腺苷的染色质重塑的生物学方面取得了重大进展。我们已经产生并分析了NURF最大亚基的突变体，发现NURF是胚胎发育到胚胎第5-6天所必需的。分子标记的原位杂交分析表明，NURF可能是结节/转化生长因子β信号通路的一部分，通往染色质。分子研究表明，NURF可以与SMAD转录因子相互作用，这为Smads的转化生长因子-β激活导致NURF募集和靶基因启动子的核小体重塑提供了一个模型。我们还在染色质重塑酶SWI2/SNF2超家族成员SWR1复合体的研究中取得了很好的进展。我们在SWR1复合体和特异组蛋白变异体H_2AZ之间建立了新的联系。组蛋白变异体H2 AZ优先结合在真核细胞染色质中的特定位置，在那里它调节染色体的功能。在酿酒酵母中，组蛋白H_2AZ的沉积是由多蛋白SWR1复合体介导的，该复合体催化依赖于ATP的核小体组蛋白H_2A与H_2AZ的交换。我们发现了一种新的H2 AZ变异体的组蛋白伴侣，它以1：1的比例与H2 AZ-H2 B二聚体结合。遗传和生化研究表明，H_2AZ由多个组蛋白伴侣蛋白稳定，这些组蛋白伴侣蛋白冗余地结合，将组蛋白变体运送到SWR1酶复合体。我们的发现为组蛋白变体交换的最早阶段提供了洞察力。

Our group has continued studies of chromatin structure and the regulation of eukaryotic gene expression. This year we have made significant progress towards understanding the biology of ATP-dependent chromatin remodeling by NURF (Nucleosome Remodeling Factor) in the mouse. We have generated and analyzed mutants for the largest subunit of NURF, and found that NURF is required for early embryonic development until embryonic day 5-6. Analysis of molecular markers by in situ hybridization indicates that NURF may be functioning as part of the nodal/TGF beta signaling pathway to chromatin. Molecular studies show that NURF can physically interact with the SMAD transcription factor, this providing a model by which TGF-beta activation of SMADs leads to NURF recruitment and nucleosome remodeling at target gene promoters.We are also making excellent progress on studies of the SWR1 complex, a member of the SWI2/SNF2 superfamily of chromatin remodeling enzymes. We established a new link between the SWR1 complex and a specific histone variant H2AZ. Histone variant H2AZ is incorporated preferentially at specific locations in eukaryotic chromatin, where it modulates chromosome functions. In S. cerevisiae, deposition of histone H2AZ is mediated by the multi-protein SWR1 complex, which catalyzes ATP-dependent exchange of nucleosomal histone H2A for H2AZ. We have discovered a new histone chaperone for the H2AZ variant, which binds the H2AZ-H2B dimers in a 1:1 ratio. Genetic and biochemical studies indicate that H2AZ is stabilized by multiple histone chaperones which bind redundantly to deliver the histone variant to the SWR1 enzyme complex. Our findings provide insight into the earliest stage of histone variant exchange.