UBC9-THE NEW PROTEIN PARTNER OF BRCA1

UBC9 is an E2 conjugating enzyme that transfers the activated SUMO (small ubiquitin-related modifier) to protein substrates, and thus it plays a key role in sumoylation. The SUMO modyfication is shown to be involved in BRCA1 regulation of gene expression and maintenance of genome stability. BRCA1 is modified by SUMO in response to genotoxic stress and co-localizes at site of DNA damage with SUMO proteins and UBC9. Analysis of UBC9 and BRCA1 proteins interactions demonstrate that UBC9 is required for BRCA1 ubiquitin ligase activity. Furthermore, UBC9 with BRCA1 are found in the nuclear foci, where the repair of DNA double-strand breaks is carried out. Interestingly, UBC9 protein interacts with BRCA1 and affects its activity not only in the context of sumoylation reaction, but also in SUMO-independent manner. Reports on these interactions between UBC9 and BRCA1 proteins show the new light on the complex process of carcinogenesis.