... requires the activity of the UPS. On the otherhand, because the above proteasome inhibitors do notprovide any information on the specific ubiquitin ligasesinvolved, we next examined the potential ... effect.We then hypothesized that if the dominant-negative activ-ity of Vpr(R80A) stems from its ability to bind to DCAF1,then introducing the Q65R mutation in Vpr(R80A) wouldabolish the dominant-negative ... fibroblasts. These results, indicate that DDB2 is dis-pensable for the induction of G2 arrest by Vpr. Thus, theseresults, together with the finding that Vpr binds toDCAF1, support the notion...