Background：

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.