Chromatin Biosynthesis: Defining the Deposition Code

描述（申请人提供）：申请人研究计划的长期目标是阐明体细胞染色质生物合成的机制，并了解表观遗传信息向后代细胞的转移。为此，本提案的重点是新合成的组蛋白（主要的染色体蛋白质）的翻译后修饰，和组蛋白修饰的复制叉，在人类细胞中的染色质复制过程中的传播。忠实复制遗传和表观遗传信息的能力对于正常细胞生长和功能至关重要。这种能力的丧失可导致发育异常和病理性细胞增殖增加。 将进行实验以确定新合成的人类组蛋白的完全乙酰化、磷酸化和甲基化状态。这将通过使用对位点特异性组蛋白修饰具有特异性的抗组蛋白抗体从胞质提取物（其在沉积到DNA上之前含有新的组蛋白）中免疫沉淀新生组蛋白来实现。新合成的组蛋白也将进行微测序，使用揭示位点特异性翻译后修饰的方法。还将通过对在不存在同时从头核小体组装的情况下复制的染色质进行免疫沉淀测定，检查预先存在的组蛋白修饰在DNA复制期间持续存在的能力。这些实验将提供有关表观遗传信息建立和代代相传的方式的基本信息。 作为上述研究的一部分，将检查HAT-B组蛋白乙酰转移酶的性质，其很可能参与乙酰化新合成的组蛋白H4。将使用修饰的组蛋白和H4 N-末端肽作为底物分析HAT-B的活性和特异性。还将使用删除了Had基因的酵母突变体进行实验，以确定这些突变体是否能够在体内乙酰化新合成的H4。最后，HAT-B酶的功能将通过全基因组mRNA的分析，在酵母裂殖酵母的hatidelete突变体进行研究。

DESCRIPTION (provided by applicant): The long-term objective of the applicant's research program is to elucidate the mechanisms of somatic chromatin biosynthesis, and to understand the transfer of epigenetic information to progeny cells. To this end, the present proposal focuses on posttranslational modifications of newly synthesized histones (the major chromosomal proteins), and the propagation of histone modifications at the replication fork, during chromatin replication in human cells. The ability to faithfully replicate genetic and epigenetic information is essential for normal cellular growth and function. Loss of this capability can result in increased developmental abnormalities, and pathological cell proliferation. Experiments will be performed to determine the complete acetylation, phosphorylation, and methylation states of newly synthesized human histones. This will be accomplished by immunoprecipitating nascent histones from cytosolic extracts (which contain new histones prior to deposition onto DNA), using anti-histone antibodies that are specific for site-specific histone modifications. Newly synthesized histones will also be microsequenced, using methods that reveal site-specific posttranslational modifications. The ability of pre-existing histone modifications to persist during DNA replication will also be examined, by performing immunoprecipitation assays on chromatin replicated in the absence of concurrent de novo nucleosome assembly. These experiments will provide fundamental information on the manner in which epigenetic information is established, and maintained from generation to generation. As part of the above studies, the properties of the HAT-B histone acetyltransferase, which very likely is involved in acetylating newly synthesized histone H4, will be examined. The activity and specificity of HAT-B will be analyzed, using modified histones and H4 N-terminal peptides as substrates. Experiments will also be performed using yeast mutants, deleted of the Had gene, to determine whether these mutants are capable of acetylating newly synthesized H4 in vivo. Finally, the function of the HAT-B enzyme will be studied through whole-genome mRNA analysis, in a hatidelete mutant of the yeast Schizosaccharomyces pombe.