ABSTRACT
This chapter demonstrates several modifications of histones to occur in vivo; the acetylation, phosphorylation, methylation, and thiolation of certain amino acids being the main ones. Histones can be acetylated in vitro in the presence of acetyl transferases and appropriate conditions. The initial studies on the biologically active chemical modification of histones opened a completely new chapter in the biochemistry of these proteins by stimulating an extensive search for chemical modifications of histones which would occur in vivo. As with other chemical modifications of the histones, methylation occurs at specific sites on the "already assembled" proteins. The chapter describes several protein methylases capable of methylating histones. The main transfer of methyl residues to chromatin histones occurs during the profound morphological changes of chromatin condensation. The chapter discusses the interaction of DNA with histones changes the DNA conformation. The time course of DNA and protein methylation suggests that the protein methylation is an intermediate step in methyl transfer to the DNA.
