SUBUNIT STRUCTURE OF CHROMATIN

这项研究的总体目标是了解 以及决定和稳定结构的相互作用 核小体和染色质的高级结构。 以来 这些结构中的可逆修饰必须伴随这种 核过程，如染色质复制和转录， 对染色质稳定性的理解对于完整的 理解这些过程如何发生和控制， vivo. 这些问题将通过使用定义明确的 模型系统 核小体和寡核小体 通过在克隆DNA上用组蛋白八聚体重建而构建 含有单个或多个定位序列的片段。 完整的鸡红细胞组蛋白或 通过受控的蛋白水解去除N-末端尾部， 被雇用。 新的方法允许用修改的 H2 A/H2 B或H3/H4。 利用这些系统，将研究以下问题： (1)什么样的组蛋白或组蛋白的一部分， 在DNA序列上定位信号 (2)解离的热力学参数是什么 一个确定的核小体在中等盐浓度？ 有哪些 特定组蛋白和组蛋白的部分对 核小体稳定性？ (3)对于延长链的精确要求是什么， 染色质中的螺线管转变？ 这些实验将利用 如上所述构建的定相的均质寡核小体。 (4)不同种类的组蛋白尾部在 稳定螺线管结构

The overall aim of this research is an understanding of the forces and interactions that determine and stabilize the structure of the nucleosome and the higher order structure of chromatin. Since reversible modification in these structures must accompany such nuclear processes as chromatin replication and transcription, an understanding of chromatin stability is essential to a complete comprehension of how these processes occur and are controlled in vivo. The problems will be approached through the use of well defined model systems. Nucleosomes and oligonucleosomes will be constructed by reconstitution with histone octamers on cloned DNA fragments containing single or multiple positioning sequences. Either intact chicken erythrocyte histones or histones from which N-terminal tails have been removed by controlled proteolysis will be employed. New methods allow reconstitution with either modified H2A/H2B or H3/H4. With such systems, the following questions will be investigated: (1) What histones, or portions of histones, recognize the positioning signals on DNA sequences? (2) What are the thermodynamic parameters for the dissociation of a defined nucleosome at moderate salt concentrations? What are the contributions of particular histones and portions of histones to nucleosome stability? (3) What are the precise requirements for the extended chain to solenoid transition in chromatin? These experiments will utilize phased, homogeneous oligonucleosomes constructed as above. (4) What roles do the different classes of histone tails play in stabilizing the solenoidal structure?