DNA deaminase (cytidine deaminase) which acts as an inhibitor of retrovirus replication and retrotransposon mobility via deaminase-dependent and -independent mechanisms. 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 against simian immunodeficiency virus (SIV), hepatitis B virus (HBV), herpes simplex virus 1 (HHV-1) and Epstein-Barr virus (EBV) and may inhibit the mobility of LTR and non-LTR retrotransposons. May also play a role in the epigenetic regulation of gene expression through the process of active DNA demethylation. a 2'-deoxycytidine in single-stranded DNA + H(+) + H2O = a 2'-deoxyuridine in single-stranded DNA + NH4(+) (Microbial infection) Antiviral activity is neutralized by the HIV-1 virion infectivity factor (Vif), that prevents its incorporation into progeny HIV-1 virions by both inhibiting its translation and/or by inducing its ubiquitination and subsequent degradation by the 26S proteasome. Homodimer (PubMed:22977230, PubMed:23001005). Interacts with TRIB3 (PubMed:22977230). Interacts with AGO2 (PubMed:22915799). (Microbial infection) Interacts with human foamy virus protein Bet; this interaction does not induce APOBEC3C degradation but prevents its dimerization and incorporation into the virion by binding of Bet close to or within the APOBEC3C dimerization site. (Microbial infection) Interacts with HIV-1 Vif. Expressed in spleen, testes, peripherical blood lymphocytes, heart, thymus, prostate and ovary. Up-regulated by IFN-alpha. 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.