The degradation of promyelocytic leukemia and Sp100 proteins by herpes simplex virus 1 is mediated by the ubiquitin-conjugating enzyme UbcH5a

infected cell protein 0 (ICPO) of herpes simplex virus 1 expresses two E3 ubiquitin (Ub) ligase activities mapping in the domains encoded by exons 2 and 3, respectively. Site 1 (exon 3) is responsible for the degradation of the E2 Ub-conjugating enzyme cdc34 whereas site2(exon 2) is associated with a ring finger and has been shown to mediate the degradation of promyelocytic leukemia (PML) and Sp 100 proteins and the dispersal of nuclear domain 10 (ND10). In in vitro assays site 2 polyubiquitylates the E2 enzymes UbcH5a and UbcH6 but not other (e.g., UbcH7) enzymes. In this article, we show that ectopic expression of dominant negative UbcH5a carrying the substitution C85A delayed or blocked the degradation of PML and Sp 100 and dispersal of ND10 whereas ectopic expression of wild-type UbcH5a or dominant negative UbcH6 and UbcH7 carrying the substitutions C131A and C86A, respectively, had no effect. These results link the degradation of PML and Sp 100 and the dispersal of ND10 to the E3 activities of ICPO associated with the UbcH5a E2 enzyme.