two forms of activationinduced cytidine deaminase differing in their ability to bind agarose background activationinduced cytidine deaminase aid is a bcellspecific 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 beadsmethodologyprincipal 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 aloneconclusionssignificance these binding characteristics may be due to the known posttranslational modifications of aid they may also need to be considered in coimmunoprecipitation experiments to avoid falsepositive results