The function of APOBEC3H (apolipoprotein B mRNA editing enzyme catalytic subunit 3H, Ensembl gene identifier ENSG00000100298) is as follows. DNA deaminase (cytidine deaminase) which acts as an inhibitor of retrovirus replication and retrotransposon mobility via deaminase- dependent and -independent mechanisms (PubMed:16571802, PubMed:16920826, PubMed:18779051, PubMed:18827027, PubMed:20062055, PubMed:22915799, PubMed:29290613). The A3H-var/haplotype 2 exhibits antiviral activity against vif-deficient HIV-1 (PubMed:18299330, PubMed:21835787, PubMed:23097438, PubMed:29290613). 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 (PubMed:18299330). 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 (PubMed:18299330). Selectively targets single-stranded DNA and does not deaminate double-stranded DNA or single- or double-stranded RNA (PubMed:20062055). Exhibits antiviral activity also against T-cell leukemia virus type 1 (HTLV-1) and may inhibit the mobility of LTR and non-LTR retrotransposons (PubMed:20062055, PubMed:22457529). {ECO:0000269|PubMed:16571802, ECO:0000269|PubMed:16920826, ECO:0000269|PubMed:18299330, ECO:0000269|PubMed:18779051, ECO:0000269|PubMed:18827027, ECO:0000269|PubMed:20062055, ECO:0000269|PubMed:21835787, ECO:0000269|PubMed:22457529, ECO:0000269|PubMed:22915799, ECO:0000269|PubMed:23097438, ECO:0000269|PubMed:29290613}.