Figure 2-14. Interactions of b subunits of unequal lengths. An epitope-tag system novel
 to F1Fo ATP synthase studies was established in order to determine whether b
 subunits of unequal length could interact to form the dimer in an intact and
 functional enzyme complex. The b subunit was expressed with a V5-
 epitope tag at its C-terminus (represented by the 's' shaped red line) and b ,
 was expressed with a histidine tag at its N-terminus (represented by the curved
 orange line). The lightning bolt indicates a deletion and the orange patch
 represents an insertion of amino acids. The histidine tag allowed for
 purification on a Nickel affinity column and the V5-tag allowed us to detect
 the presence of the b subunit after Ni-purification using Western blot
 analysis. Expression of the two different epitope-tagged b subunits in the
 same cell leads to three distinct interactions within an F1Fo ATP synthase
 complex (1) a homodimer of b z_,, (2) a homodimer of b+7-his and (3) a
 heterodimer consisting of both the shortened and lengthened b subunit.