Three phenotypically distinct processes-somatic hypermutation, gene conversion, and switch recombination-remodel the functionally rearranged immunoglobulin (Ig) loci in B cells. Somatic hypermutation and switch recombination have recently been shown to depend on the activation-induced deaminase (AID) gene product. Here, we show that the disruption of the AID gene in the chicken B cell line DT40 completely blocks Ig gene conversion and that this block can be complemented by reintroduction of the AID complementary DNA. This demonstrates that the AID master gene controls all B cell-specific modifications of vertebrate Ig genes.
