Two Forms of Activation-Induced Cytidine Deaminase Differing in Their Ability to Bind Agarose

BACKGROUND: Activation-induced cytidine deaminase (AID) is a B-cell-specific DNA mutator that plays a key role in the formation of the secondary antibody repertoire in germinal center B cells. In the search for binding partners, protein coimmunoprecipitation assays are often performed, generally with agarose beads. METHODOLOGY/PRINCIPAL FINDINGS: We found that, regardless of whether cell lysates containing exogenous or endogenous AID were examined, one of two mouse AID forms bound to agarose alone. CONCLUSIONS/SIGNIFICANCE: These binding characteristics may be due to the known post-translational modifications of AID; they may also need to be considered in coimmunoprecipitation experiments to avoid false-positive results.