AN ESSENTIAL UBIQUITIN-CONJUGATING ENZYME WITH TISSUE AND DEVELOPMENTAL SPECIFICITY IN THE NEMATODE CAENORHABDITIS-ELEGANS

The ubc-2 gene in Caenorhabditis elegans encodes a ubiquitin-conjugati ng enzyme (E2) homologous to yeast UBC4 and UBC5. UBC4 and UBC5 are in dividually dispensable class I E2 enzymes involved in the degradation of short-lived and abnormal proteins. Transgenic analysis using ubc-2- lacZ fusions and in situ immunofluorescence indicate that ubc-2 is abu ndantly expressed in most tissues of embryos and early larvae, but bec omes specific to the nervous system in L4 larvae and adults. This sugg ests that the functions of this type of E2 are developmentally regulat ed in C.elegans. This hypothesis is supported by antisense analysis, w hich shows that blocking the expression of ubc-2 has a more severe eff ect in early developmental stages than in later stages. Through comple mentation of previously identified essential genes in the vicinity of ubc-2, we demonstrate that ubc-2 corresponds to let-70, a gene essenti al for C.elegans larval development. One let-70(ubc-2) allele contains a His75-->Tyr substitution, while another has an altered splice donor site.