THE MUBC9 MURINE UBIQUITIN-CONJUGATING ENZYME INTERACTS WITH THE E2A TRANSCRIPTION FACTORS

The ubiquitin-mediated degradation of cellular proteins requires the s equential activity of E1, E2 and, in some cases, E3 enzymes. Using the yeast two-hybrid system, we have cloned 1.0- and 2.5-kb cDNAs encodin g the identical murine E2, or ubiquitin conjugating enzyme by virtue o f its interaction with the E2A transcription factor. This cDNA encodes the 158-amino-acid protein, mUBC9, which has considerable sequence ho mology to UBC9 from Saccharomyces cerevisiae and HUS5 from Schizosacch aromyces pombe and is identical to the human UBC9 protein. HUS5 is ess ential for DNA damage repair, whereas UBC9 is necessary for G2/M progr ession. The human protein has been shown to correct the UBC9 defect in yeast. Antisera raised against bacterially expressed mUBC9 fusion pro tein recognize a murine cellular protein of approximately 18 kDa, corr esponding to the predicted mobility. Unlike E2A, the mUBC9 protein lev el is not regulated by serum growth factors. The activity of the appar ent homologues UBC9 and HUS5 suggests that mUBC9 may be involved in th e degradation of key nuclear proteins that regulate cell cycle progres sion. (C) 1997 Elsevier Science B.V.