Deamination of cytidine residues in single-stranded DNA (ssDNA) is an important mechanism by which apolipoprotein B mRNA-editing, catalytic polypeptide-like (APOBEC) enzymes restrict endogenous and exogenous viruses. The dynamic process underlying APOBEC-induced hypermutation is not fully understood. Here we show that enzymatically active APOBEC3G can be detected in wild-type Vif(+) HIV-1 virions, albeit at low levels. In vitro studies showed that single enzyme-DNA encounters result in distributive deamination of adjacent cytidines. Nonlinear translocation of APOBEC3G, however, directed scattered deamination of numerous targets along the DNA. Increased ssDNA concentrations abolished enzyme processivity in the case of short, but not long, DNA substrates, emphasizing the key role of rapid intersegmental transfer in targeting the deaminase. Our data support a model by which APOBEC3G intersegmental transfer via monomeric binding to two ssDNA segments results in dispersed hypermutation of viral genomes.
Bibliographical noteFunding Information:
This work was carried out in the Krueger Laboratory with the support of N. and L. Glick, and P. and M. Weiss. We thank K. Strebel (US National Institutes of Health (NIH), Bethesda, Maryland, USA) for providing pcDNA-APOBEC3G. We thank E. Pikarsky, R. Harris and H. Matsuo for constructive and helpful discussion, and S. Amir for editing this manuscript. Anti-APOBEC3G-C-terminal antibody was obtained from J. Lingappa through the NIH AIDS Research and Reference Reagent Program, Division of AIDS, NIAID, NIH. This work was supported in part by the Israel Ministry of Industry Trade & Labor via the Nofar program, the Israel Ministry of Health and the United States-Israel Binational Science Foundation (BSF).