Determination of the pro-Ac45 cleavage site. (A) Schematic representation of the different constructs. A FLAG epitope tag was inserted C-terminally of Arg-219 (RfRR), Arg-222 (RRfR), Arg-225 (RRRf), or Val-243 (VfA). RRRf was used as template to generate Ala-219-P-S-Ala-222-V-A-Ala-225-FLAG (AAAf). (B) RPE.40 cells were transfected with the different constructs in the presence or absence of a furin expression construct. (Upper) After radiolabeling, the lysates were divided in two, of which one half was immunoprecipitated with M2 antibody as a control for efficient expression of the construct. (Lower) Immunoprecipitation with M1 of cleaved Ac45 is shown. Results shown for the processing of AAAf are from an independent experiment. Molecular masses are indicated (kDa).