coiled-coil of similar length as determined from its frictional coefficient (1.60) in an

ultracentrifuge and from NMR relaxation parameters (192). Secondly, small-angle X-ray

scattering by b52-122 in Solution specified a maximum length to be about 95 A+, consistent

with the expected coiled-coil length (13). Thirdly, CD spectroscopy indicated that this

polypeptide was 100% ot-helical and the similar intensities of the minima suggested the

helices to be arranged in a coiled-coil (204). Fourthly, cysteine substitution and

crosslinking studies suggested a periodicity consistent with a parallel coiled-coil (Figure

1-5) (204). Finally, b subunit sequence analysis of E coli and other prokaryotes revealed

a conservation of an undecad pattern, which is a distinctive characteristic of a right-

handed coiled coil. Mutation of amino acid residue barg-83, which interrupts the undecad

repeat, markedly stabilized the dimer, as expected for the proposed two-stranded, right-

handed coiled-coil structure.

 The carboxyl-terminal F1-binding domain, bl24-156, alSo referred to as the 6-binding

domain, has a more globular conformation and is required for the binding of F1 to Fo

(205, 206). Work accomplished by Futai and coworkers two decades ago revealed that

truncation of the extreme carboxyl-terminus of the F1-binding domain by only a few

amino acids resulted in assembly defects in F1Fo ATP synthase (206). Subsequently,

work performed by Dunn and coworkers demonstrated that the final two to four amino

acids of the b subunit were necessary for binding the 6 subunit of Fl (205). An addition

of a cysteine at the carboxyl-terminus was chemically crosslinked to a cysteine

introduced at Siss.

 A close association of the two b subunits in the F1-binding domain was indicated

by crosslinks formed between cysteines individually substituted at positions bl24, bl25,