DDB1 and HIV-1 infection: To test whether the Vpr-mediated enhancement of single-cycle HIV-1 infection involved the DDB1/DCAF1/Cul4A complex and proteasomal degradation, DCAF1 was transiently knocked down in HuT/CCR5 cells using lentiviral vectors expressing shRNA-specific to DCAF1 and a scrambled shRNA vector was used as a control (Fig. 6A).