Caenorhabditis elegansUBC-1, a Ubiquitin-Conjugating Enzyme Homologous to Yeast RAD6/UBC2, Contains a Novel Carboxy-Terminal Extension That Is Conserved in Nematodes

摘要

ABSTRACTTheRAD6/UBC2gene fromSaccharomyces cerevisiaeencodes a ubiquitin-conjugating enzyme involved in DNA repair, induced mutagenesis, and sporulation. Here we report the isolation and characterization of theCaenorhabditis elegans RAD6homolog designatedubc-1. Ubc-1encodes a 21.5-kD protein that shares considerable identity with RAD6 (66) as well as with otherRAD6homologs, includingSchizosaccharomyces pomberhp6+ (70),Drosophila melanogasterDhr6 (83), and the two human homologs HHR6A and HHR6B (84 and 83, respectively). However, UBC-1 is distinct in being the only known RAD6 homolog, other than RAD6 itself, with a carboxy-terminal extension. Analysis of UBC-1 homologs from C.briggsaeandAscaris suumshow that the presence of the carboxy-terminal extension is conserved in nematodes. When constitutively expressed from the yeast promoterADH1, ubc-1complements the DNA repair functions in aS. cerevisiae rad6▲ mutant. Surprisingly,ubc-1fails to complement the sporulation function ofRAD6, despite its possession of an acidic carboxy-terminal tail.C. elegansUBC-1 is capable of forming a thiol-ester bond with ubiquitin, but, unlike RAD6, is unable to transfer ubiquitin to histone H2Bin vitro. Both eis andtranssplicing are involved in the maturation of theubc-1transcript. The presence of the SL2irans-splice leader in theubc-1transcript suggests thatubc-1may be co-transcribed as part of a polycistronic messag