Intensity of Deoxycytidine Deamination of HIV-1 Proviral DNA by the Retroviral Restriction Factor APOBEC3G Is Mediated by the Noncatalytic Domain

APOBEC3G is a single-stranded (ss) DNA deaminase that restricts replication of HIV-1 by inducing viral genome mutagenesis through deamination of cytosine to uracil on HIV-1 cDNA. APOBEC3G has polydisperse oligomeric states and deaminates ssDNA processively through jumping and sliding. APOBEC3G has a catalytically inactive N-terminal CD1 domain that mediates processivity and an active C-terminal CD2 domain that catalyzes deaminations. Here, we assess the determinants of APOBEC3G deamination efficiency mediated by the CD1 domain by comparing native APOBEC3G and two CD1 mutants, a monomeric mutant (F126A/W127A) and a clinical mutant associated with high viral loads (H186R). Biochemical assays on ssDNA or partially dsDNA and with a reconstituted HIV replication system demonstrate that both mutants of Apo3G have altered DNA scanning properties in either jumping (F126A/W127A) or sliding (H186R), which results in decreased abilities to induce mutagenesis during reverse transcription. The data reveal a functionality for Apo3G oligomers in deamination and provide the first biochemical characterization of the clinical mutant H186R. The data demonstrate that the balance between the jumping and sliding of Apo3G is needed for efficient mutational inactivation of HIV-1.