分子生物学（双语）10 Chromatin.ppt

Chapter 10 Chromatin;;Individual nucleosomes are released by digestion of chromatin with micrococcal nuclease. The bar is 100 nm; Basic Structures ;10 nm fiber – A linear array of nucleosomes generated by unfolding from the natural condition of chromatin. linker histones – A family of histones (such as histone H1) that are not components of the nucleosome core. Linker histones bind nucleosomes and/or linker DNA and promote 30 nm fiber formation. ;The 10 nm fiber in partially unwound state can be seen to consist of a string of nucleosomes;The 10 nm fiber is a continuous string of nucleosomes;30 nm fiber – A coil of nucleosomes. It is the basic level of organization of nucleosomes in chromatin. nonhistone – Any structural protein found in a chromosome except one of the histones. ;The 30 nm fiber has a coiled structure;The 30 nm fiber is a two start helix consisting of two rows of nucleosomes coiled into a solenoid; DNA Is Organized in Arrays of Nucleosomes ;Micrococcal nuclease digests chromatin in nuclei into a multimeric series of DNA bands that can be separated by gel electrophoresis. Each multimer of nucleosomes contains the appropriate number of unit lengths of DNA;Footprinting: Characterizing RNA Polymerase–Promoter and DNA–Protein Interactions ;FIGURE 05: Micrococcal nuclease initially cleaves between nucleosomes;The nucleosome is a cylinder with DNA organized into ~1 2/3 turns around the surface;DNA occupies most of the outer surface of the nucleosome;Sequences on the DNA that lie on different turns around the nucleosome may be close together;The nucleosome consists of approximately equal masses of DNA and histones (including H1);Possible model for the interaction of histone H1 with the nucleosome;;;; The Nucleosome Is the Subunit of All Chromatin;The crystal structure of the histone core octamer is represented in a space-filling model;Linker DNA is the region of 8 to 114 bp, and this is the region that is susceptible to early cleavage by the enzyme. Changes i