K-bZIP is able to SUMOylate IRF-1 and IRF-2 and to interact with IRF-7. Flag-tagged IRF-1 (A), IRF-2 (B) and IRF-7 (C) were transiently co-transfected with the indicated tagged constructs. Total cell lysates (TCLs) were prepared 48 hours after transfection. The lysates were immunoprecipitated with M2-beads and analyzed by immunoblotting using anti-IRF-1 (A; right panel), anti-IRF-2 (B; right panel), anti-SUMO-2/3 (A and B; left panel) and anti-IRF-7 (C) antibodies. (D) TCLs from TREx-F3H3-K-bZIP BCBL-1 cells before and after 48 hours of Dox induction for K-bZIP overexpression were used for immunoprecipitation with anti-K-bZIP antibody. The immunoprecipitates and TCLs were analyzed by immunoblot with antibodies as indicated.