DNA deaminase (cytidine deaminase) which acts as an inhibitor of retrovirus replication and retrotransposon mobility via deaminase-dependent and -independent mechanisms. The A3H-var/haplotype 2 exhibits antiviral activity against vif-deficient HIV-1. After the penetration of retroviral nucleocapsids into target cells of infection and the initiation of reverse transcription, it can induce the conversion of cytosine to uracil in the minus-sense single-strand viral DNA, leading to G-to-A hypermutations in the subsequent plus-strand viral DNA. The resultant detrimental levels of mutations in the proviral genome, along with a deamination-independent mechanism that works prior to the proviral integration, together exert efficient antiretroviral effects in infected target cells. Selectively targets single-stranded DNA and does not deaminate double-stranded DNA or single- or double-stranded RNA. Exhibits antiviral activity also against T-cell leukemia virus type 1 (HTLV-1) and may inhibit the mobility of LTR and non-LTR retrotransposons. a 2'-deoxycytidine in single-stranded DNA + H(+) + H2O = a 2'-deoxyuridine in single-stranded DNA + NH4(+) Antiviral activity is neutralized by the HIV-1 virion infectivity factor (VIF), that prevents its incorporation into progeny virions by both inhibiting its translation and/or by inducing its ubiquitination and subsequent degradation by the 26S proteasome. Interacts with AGO1, AGO2 and AGO3. Haplotype 1 is distributed in both the nucleus and cytoplasm, whereas haplotype 2 is predominantly cytoplasmic. Expressed in lymphoid organs. Also detected in non-lymphoid tissues including lung, testis, ovary, fetal liver and skin. There are at least 4 different haplotypes in the human population. The allele A3H-var/haplotype 2 encodes a more stable protein which is able to block HIV-1 replication. The displayed allele (haplotype 1) is unstable and inefficient to block HIV-1 replication. APOBEC3H from old world monkeys has retained its antiviral activity, while it is lost in other primates. It is one of seven related genes or pseudogenes found in a cluster, thought to result from gene duplication, on chromosome 22. Belongs to the cytidine and deoxycytidylate deaminase family.