Chromatin Remodeling and Histone Acetylation

In order to make theDNAtemplate available for both replication and transcription, the chromatin is “remodeled.” One way to accomplish this reversible process is by altering the electrostatic interaction with histone. Acetylation of lysine residues (and to some extent phosphorylation of serine and threonine residues) reduces the binding affinity of histones with DNA in nucleosome cores and may thus allow exposure of free DNA to the transcriptional machinery. Additionally, a more complex energy-driven process involving the proteins SNF1 andSWIcauses a major alteration of the chromatin structure, which is necessary for reprogramming of the transcriptional regimen during growth, development, and associated differentiation. DNA replication also requires access of DNA in free form to the replication machinery and, therefore, may also be dependent on the same remodeling process and could even require dissociation and reassociation of the nucleosome core.