DNA deaminase (cytidine deaminase) which acts as an inhibitor of retrovirus replication and retrotransposon mobility via deaminase-dependent and -independent mechanisms. May also play a role in the epigenetic regulation of gene expression through the process of active DNA demethylation (By similarity). a 2'-deoxycytidine in single-stranded DNA + H(+) + H2O = a 2'-deoxyuridine in single-stranded DNA + NH4(+) Homodimer. Interacts with TRIB3 (By similarity). Belongs to the cytidine and deoxycytidylate deaminase family.