K921 of Abl is modified by acetylation following DNA strand breaks. (a) Structure of c-Abl with the consensus acetylation sequence (mouse and human) located in the DNA-binding domain (DBD) is shown. (b) Abl-/- 3T3 cells, reconstituted with Flag-tagged WT or K>R (921, 924) mutants of Abl, were either mock-treated or exposed to 5Gy of IR. Anti-Flag immunoprecipitates were prepared and immune-analyzed with acetyl-lysine (top panel) or Flag antibody (bottom panel). (c) Immunoblot, shown in panel A, was reprobed against K921 site-specific acetyl-Abl antibody (top panel). An aliquot of the lysate was also immune-analyzed with anti-Flag antibody (bottom panel). (d) Bleomycin induces K921 Abl acetylation. Abl-/-3T3 cells reconstituted with vector or Flag-tagged Abl were exposed to bleomycin (10 μM; 1 h) and lysates, prepared 4 h later, were subjected to immunoblotting with K921 acetyl Abl (top panel) or anti-Flag (bottom pane l) antibody.