Single-stranded DNA-specific cytidine deaminase. Involved in somatic hypermutation (SHM), gene conversion, and class-switch recombination (CSR) in B-lymphocytes by deaminating C to U during transcription of Ig-variable (V) and Ig-switch (S) region DNA. Required for several crucial steps of B-cell terminal differentiation necessary for efficient antibody responses. May also play a role in the epigenetic regulation of gene expression by participating in DNA demethylation. a 2'-deoxycytidine in single-stranded DNA + H(+) + H2O = a 2'-deoxyuridine in single-stranded DNA + NH4(+) Interacts with CTNNBL1; the interaction is important for the immunoglobulin switch activity of AICDA. Interacts (via its NLS) with KPNA1. Interacts with PKA/PRKACA and PRKAR1A/PKR1. Interacts with SUPT6H, TRIM28 and NCL. Directly interacts with MCM3AP; this interaction may favor AICDA recruitment to immunoglobulin variable region genes, hence promoting somatic hypermutations (By similarity). Predominantly cytoplasmic. In the presence of MCM3AP/GANP, relocalizes to the nucleus. Expressed in lymph nodes, spleen and thymus. Ser-38 is the major site whereas Thr-27 is the minor site of phosphorylation. Phosphorylation regulates its class-switch recombination activity (By similarity). Probably monoubiquitinated on several residues by RNF126. Belongs to the cytidine and deoxycytidylate deaminase family.