Biochemistry Seminar: Testing the "Histone Code" Hypothesis Using Synthesis

Abstract

Robert McGinty, Champak Chatterjee and Tom W. Muir

DNA in eukaryotic cells is packaged into chromatin. The fundamental unit of this chromatin is the nucleosome that is made up of 146 base pairs of DNA wrapped around a histone core octamer containing two copies of each histone (H2A, H2B, H3 and H4). The packaging of these nucleosomes into higher-order chromatin structures is a key determinant of gene expression making histone biology fundamental to all processes within a living organism. An ever-increasing body of information indicates that posttranslational modification of histone proteins is one way local chromatin structure is manipulated. These modifications affect their influence through changes in nucleosome structure, as well as recruitment of additional protein factors that mediate downstream functions. One such modification, ubiquitylation, occurs on histones 2A and 2B, has been implicated in gene transcription and in methylation of lysines 4 and 79 of histone 3. The mechanism by which this "crosstalk" occurs is unclear, primarily due to the inability to generate or isolate homogeneous ubiquitylated nucleosomes for biochemical studies. Here, we report the semisynthesis of homogeneous ubiquitylated H2B and its incorporation into nucleosomes and nucleosome arrays. Access to this "designer chromatin" has allowed functional dissection of methylation of K79 by the methyltransferase, hDot1. Mechanistic insights from these studies will be discussed.

Coffee and Tea 11:45 AM   
Lecture begins 12:00 PM