Histone ubiquitination: triggering gene activity.

Recently, many of the enzymes responsible for the addition and removal of ubiquitin from the histones H2A and H2B have been identified and characterized. From these studies, it has become clear that H2A and H2B ubiquitination play critical roles in regulating many processes within the nucleus, including transcription initiation and elongation, silencing, and DNA repair. In this review, we present the enzymes involved in H2A and H2B ubiquitination and discuss new evidence that links histone ubiquitination to other chromatin modifications, which has provided a model for the role of H2B ubiquitination, in particular, in transcription initiation and elongation.