DNA deaminase (cytidine deaminase) which acts as an inhibitor of retrovirus replication and retrotransposon mobility. 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 (By similarity). a 2'-deoxycytidine in single-stranded DNA + H(+) + H2O = a 2'-deoxyuridine in single-stranded DNA + NH4(+) Assembly into ribonucleoprotein complexes of high-molecular-mass (HMM) inhibits its enzymatic activity. Homodimer. Mainly cytoplasmic, small amount are found in the nucleus. 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. Belongs to the cytidine and deoxycytidylate deaminase family.