CAENORHABDITIS-ELEGANS UBC-1, A UBIQUITIN-CONJUGATING ENZYME HOMOLOGOUS TO YEAST RAD6 UBC2, CONTAINS A NOVEL CARBOXY-TERMINAL EXTENSION THAT IS CONSERVED IN NEMATODES/

The RAD6/UBC2 gene from Saccharomyces cerevisiae encodes a ubiquitin-c onjugating enzyme involved in DNA repair, induced mutagenesis, and spo rulation, Here we report the isolation and characterization of the Cae norhabditis elegans RAD6 homolog designated ubc-1, Ubc-1 encodes a 21, 5-kD protein that shares considerable identity with RAD6 (66%) as well as with other RAD6 homologs, including Schizosaccharomyces pombe rhp6 (+) (70%), Drosophila melanogaster Dhr6 (83%), and the two human homol ogs HHR6A and HHR6B (84% and 83%, respectively), However, UBC-1 is dis tinct in being the only known RAD6 homolog, other than RAD6 itself, wi th a carboxy-terminal extension, Analysis of UBC-1 homologs from C, br iggsae and Ascaris suum show that the presence of the carboxy-terminal extension is conserved in nematodes, When constitutively expressed fr om the yeast promoter ADH1, ubc-1 complements the DNA repair functions in a S, cerevisiae rad6 Delta mutant, Surprisingly, ubc-1 fails to co mplement the sporulation function of RAD6, despite its possession of a n acidic carboxy-terminal tail, C, elegans UBC-1 is capable of forming a thiol-ester bond with ubiquitin, but, unlike RAD6, is unable to tra nsfer ubiquitin to histone H2B in vitro, Both cis and trans splicing a re involved in the maturation of the ubc-1 transcript. The presence of the SL2 trans-splice leader in the ubc-1 transcript suggests that ubc -1 may be co-transcribed as part of a polycistronic message.