Lane 10). The only mechanism for recovery of bwt-vs was through dimerization with

b+124-130-his, indicating that the bwt-his subunit rescued some of the defective b subunit and

formed heterodimeric F1Fo ATP synthase complexes. Therefore, coexpression of the two

different b subunits in the same cell led to two distinct interactions within an intact F1Fo

ATP synthase complex (Figure 3-6C): 1) a homodimer of bwt-vs and 2) a heterodimer

consisting of both the defective and wild type b subunit.

 F1-ATP hydrolysis activity of total membrane protein was used as a test of F1Fo

ATP synthase assembly (Table 3-1). As expected, membranes with enzyme complexes

incorporated with b+124-130-his displayed a specific activity similar to the negative control,

indicating virtually no interaction with Fl. Coexpression of pTAM3 8 (b+124-130-his) and

pTAM46 (bwt-vs) resulted in a specific activity similar to the wild type strain (Table 3-1).

It was likely that the F1Fo ATP synthase complexes incorporated with the b+124-130-his/bwt-

vs were intact. An indication of coupled activity was shown by F1Fo ATP synthase-

mediated ATP-driven proton pumping activity in membrane vesicles prepared from the

epitope-tagged mutants (Figure 3-7). Membranes containing only the b+124-130-his subunit

exhibited no coupled activity as expected. Membranes isolated from cells coexpressing

pTAM3 8 (b+124-130-his) and pTAM46 (bwt-vs) displayed virtually the same amount of

coupled activity as the membranes from cells coexpressing bwt-vs and bwt-his. Since

coexpression of the two different b subunits in the same cell led to only two distinct

interactions, it was likely that the F1Fo ATP synthase complexes incorporated with the

b+124-130-his/bwt-vs were functional.