Activation-induced cytidine deaminase, also known as
AICDA and AID, is a 24
kDa enzyme which in humans is encoded by the
AICDA gene. It creates mutations in
DNA by
deamination of
cytosine base, which turns it into
uracil (which is recognized as a
thymine). In other words, it changes a C:G base pair into a U:G mismatch. The cell's
DNA replication machinery recognizes the U as a T, and hence C:G is converted to a T:A base pair. During
germinal center development of
B lymphocytes, AID also generates other types of mutations, such as C:G to A:T. The mechanism by which these other mutations are created is not well-understood.