DNA deaminase (cytidine deaminase) which acts as an inhibitor of retrovirus replication and retrotransposon mobility via deaminase-dependent and -independent mechanisms (PubMed:16920826, PubMed:20062055, PubMed:21835787). Exhibits antiviral activity against 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 (PubMed:16920826). 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. Inhibits also the mobility of LTR and non-LTR retrotransposons (PubMed:27428332). (Microbial infection) Enhances hepatitis B virus/HBV replication by excluding restriction factors APOBEC3F and APOBEC3G from HBV capsids. 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 virions by both inhibiting its translation and/or by inducing its ubiquitination and subsequent degradation by the 26S proteasome. Can form homo- and heterodimers with APOBEC3F and APOBEC3G (PubMed:16920826, PubMed:27289067). Interacts with L1RE1; this interaction inhibits LINE-1 retrotransposition (PubMed:27428332). (Microbial infection) Interacts with HIV-1 Vif (PubMed:16920826, PubMed:23001005). This interaction triggers APOBEC3D polyubiquitylation and degradation by the 26S proteasome (PubMed:16920826). Expressed in lymphoid organs. Also detected in non-lymphoid tissues including lung. The CMP/dCMP deaminase domain 1 mediates RNA binding, RNA-dependent oligomerization and virion incorporation whereas the CMP/dCMP deaminase domain 2 confers deoxycytidine deaminase activity and substrate sequence specificity. 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.