Activation-induced cytidine deaminase links class switch recombination and somatic hypermutation.

Activation-induced cytidine deaminase (AID), a putative RNA-editing cytidine deaiminase that is expressed strictly in activated B cells, is indispensable in three apparently distinct genetic alterations of immunoglobulin genes-namely, class switch recombination, somatic hypermutation, and gene conversion. Recent findings led us to propose a common DNA cleaving mechanism, in which the transient secondary structure of the S and V region DNA is recognized by a nicking enzyme regulated by the putative RNA-editing activity of AID.