Ring Finger Protein 20 (RNF20)

E3 ubiquitin-protein ligase BRE1A shares similarity with BRE1 of S. cerevisiae. Yeast BRE1 is a ubiquitin ligase required for the ubiquitination of histone H2B and the methylation of histone H3. In cells lacking the euchromatin-associated histone variant H2A.Z, Bre1, Rad6, and Lge1 were each essential for cell viability, supporting redundant functions for H2B ubiquitination and H2A substitution in the formation of active chromatin. Analysis of mutants demonstrated a function for Bre1/Lge1-dependent H2B monoubiquitination in the control of cell size. Reduction of BRE1A by RNA interference decreased endogenous H2B ubiquitylation, activator-dependent transcription, and H3 lys4 and lys79 methylation. BRE1A interacted with p53 (TP53) directly and was recruited to the MDM2 promoter in a p53-dependent manner.