Identification of AID-interacting proteins. (A) Silver staining of proteins coimmunoprecipitated with mouse AID-GFP-FLAG (mAID-GF), human AID-GF (hAID-GF), GF, and P13-GF from cytosolic extracts prepared from CH12F3-2A cells expressing either of the AID-GFs. Bands were excised and analyzed by MS. Proteins that appeared to be obviously more abundant in mAID-GF and hAID-GF are indicated. Nucleolin appears at two positions owing to possible modification. (B) Western blot analyses of immunoprecipitates with anti-FLAG M2 antibody from mAID-GF–expressing CH12F3-2A extracts treated with DNase I (lane 2) or RNase A (lane 3). Immunoprecipitates from untreated extracts are shown in lane 1. (C) Western blot analyses of immunoprecipitates either with anti-FLAG M2 antibody or with mouse IgG from cytosolic extracts prepared from CH12F3-2A cells expressing mAID-GF (lane 1) or GF (lane 2). Arrows indicate mAID-GF or GF. (D) Western blot analyses of immunoprecipitates with anti-Spt6 mAb from cytosolic extracts prepared from CH12F3-2A cells expressing mAID-GF (lane 1), hAID-GF (lane 2), or GF (lane 3). Two nonspecific bands appeared in input by FLAG Western blot.