Figure 1.

AID interacts with PTBP2. (a) Schematic representation of the AID expression construct (biotagDM-AID). The lysine that is biotinylated by BirA is indicated with an asterisk. The H56R,E58Q mutation inactivates the DNA deaminase activity of AID. (b) Protein extracts derived from stimulated CH12^BirA or CH12^{BirA/biotagDM-AID} cells were analyzed on immunoblots with AID antibodies. (c) Cell extracts from CH12^BirA or CH12^{BirA/biotagDM-AID} were incubated with streptavidin-agarose beads and bound proteins analyzed by immunoblotting with AID antibodies (upper) or streptavidin-coupled to horseradish-peroxidase (SA-HRP, lower). (d) DM-AID binds to S_μ. Cross-linked DNA protein complexes from unstimulated or CIT-stimulated CH12^{BirA/biotagDM-AID} cells were subjected to modified ChIP in which steptavidin-agarose replaced antibodies used in conventional ChIP. Three-fold dilutions of DNA bound to streptavidin agarose were analyzed by PCR for the presence of S_μ or the μ promoter. (e-f) Whole cell extracts derived from anti-CD40+IL-4-stimulated wild-type or AID-deficient mouse splenic B cells were immunoprecipitated with AID (e) or PTBP2 (f) antibodies and the immunoprecipitates were probed with anti-PTBP2 or anti-AID, respectively on immunoblots. E1 and E2 are two elutions of bound proteins. The data are representative of two independent experiments.