Two opposing models have been proposed for AID to deaminate either DNA or RNA. Although most data supports DNA deamination, there is no physical evidence for uracils in immunoglobulin genes. Here we demonstrate their presence by determining the sensitivity of DNA to digestion with uracil DNA glycosylase and abasic endonuclease. Using several methods of detection, we identified uracils in the variable and switch regions. Uracils were generated within 24 hours after B cell stimulation, were found on both DNA strands, and were enriched in hotspot motifs. This data provides direct evidence for the model that AID functions by deaminating cytosine in DNA. In addition, we have shown the XRCC1 protein is involved in repairing the uracils.

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National Institute on Aging
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Saribasak, Huseyin; Gearhart, Patricia J (2012) Does DNA repair occur during somatic hypermutation? Semin Immunol 24:287-92
Saribasak, Huseyin; Maul, Robert W; Cao, Zheng et al. (2011) XRCC1 suppresses somatic hypermutation and promotes alternative nonhomologous end joining in Igh genes. J Exp Med 208:2209-16
Maul, Robert W; Saribasak, Huseyin; Martomo, Stella A et al. (2011) Uracil residues dependent on the deaminase AID in immunoglobulin gene variable and switch regions. Nat Immunol 12:70-6
Kohli, Rahul M; Maul, Robert W; Guminski, Amy F et al. (2010) Local sequence targeting in the AID/APOBEC family differentially impacts retroviral restriction and antibody diversification. J Biol Chem 285:40956-64
Maul, Robert W; Gearhart, Patricia J (2009) Women, autoimmunity, and cancer: a dangerous liaison between estrogen and activation-induced deaminase? J Exp Med 206:11-3
Kohli, Rahul M; Abrams, Shaun R; Gajula, Kiran S et al. (2009) A portable hot spot recognition loop transfers sequence preferences from APOBEC family members to activation-induced cytidine deaminase. J Biol Chem 284:22898-904