The relation between DNA and histone is maintained, in part, by electrostatic bonds between positively charged histones and the negatively charged DNA. This chromatin structure commonly precludes transcription factor binding to DNA and underscores the importance of enzymes that modify histone-DNA interactions. Most modifications of the nucleosome occur on amino acid residues along the histone tail that protrudes through the DNA, and is thus vulnerable to enzymatic modification (Figure 3). The relevant histone modifications include acetylation, phosphorylation, ribosylation, and methylation. Each of these modifications can alter the interaction between the histones and the DNA, and thus alter gene expression. Our focus is on histone acetylation, which is closely associated with gene expression.
