A, schematic of fusion proteins used for luciferase complementation. B, model of PP2A/ Bβ2 interaction with the TOM translocase complex. C- and N-terminal fragments of luciferase (NLuc and CLuc) reconstitute an active enzyme when their fusion partners Bβ2 and TOM22 interact. C, complementation between CLuc-Aα and Bβ2-NLuc in intact, transiently transfected COS-M6 cells is unaffected by the K2A mutation. D, binding to TOM22 requires Lys2 of Bβ2 (significant difference, p > 0.001 by Student's t test). The bar graphs show average luciferase activities ± S.E. from triplicate cotransfections of the indicated fusion proteins. C and D, the immunoblots with a pan-B subunit antibody were performed on cells lysed after the luciferase assays and show equal expression levels of wild-type and mutant Bβ2-NLuc. The position of the 97-kDa marker is shown.