This gene is a member of the cytidine deaminase gene family. It is one of seven related genes or pseudogenes found in a cluster, thought to result from gene duplication, on chromosome 22. Members of the cluster encode proteins that are structurally and functionally related to the C to U RNA-editing cytidine deaminase APOBEC1. The protein encoded by this gene lacks the zinc binding activity of other family members. The protein plays a role in immunity, by restricting transmission of foreign DNA such as viruses. One mechanism of foreign DNA restriction is deamination of foreign double-stranded DNA cytidines to uridines, which leads to DNA degradation. However, other mechanisms are also thought to be involved, as anti-viral effect is not dependent on deaminase activity. Two transcript variants encoding different isoforms have been found for this gene.APOBEC3A (Apolipoprotein B MRNA Editing Enzyme Catalytic Subunit 3A) is a Protein Coding gene. Among its related pathways are mRNA Editing- C to U Conversion and Gene Expression. GO annotations related to this gene include hydrolase activity, acting on carbon-nitrogen (but not peptide) bonds, in cyclic amidines and deoxycytidine deaminase activity. An important paralog of this gene is APOBEC3B.