Abstract
Encapsidation of host restriction factor APOBEC3G (A3G) into vif-deficient human immunodeficiency virus type 1 (HIV-1) blocks virus replication at least partly by C-to-U deamination of viral minus-strand DNA, resulting in G-to-A hypermutation. A3G may also inhibit HIV-1 replication by reducing viral DNA synthesis and inducing viral DNA degradation. To gain further insight into the mechanisms of viral inhibition, we examined the metabolism of A3G-exposed viral DNA. We observed that an overall 35-fold decrease in viral infectivity was accompanied by a five- to sevenfold reduction in viral DNA synthesis. Wild-type A3G induced an additional fivefold decrease in the amount of viral DNA that was integrated into the host cell genome and similarly reduced the efficiency with which HIV-1 preintegration complexes (PICs) integrated into a target DNA in vitro. The A3G C-terminal catalytic domain was required for both of these antiviral activities. Southern blotting analysis of PICs showed that A3G reduced the efficiency and specificity of primer tRNA processing and removal, resulting in viral DNA ends that are inefficient substrates for integration and plus-strand DNA transfer. However, the decrease in plus-strand DNA transfer did not account for all of the observed decrease in viral DNA synthesis associated with A3G. These novel observations suggest that HIV-1 cDNA produced in the presence of A3G exhibits defects in primer tRNA processing, plus-strand DNA transfer, and integration.