F1 I:Cl j' ~I F1






 bZi b .i





Figure 6-2. Model of rotation inhibition due to a fusion protein on the a subunit. A
 natural 200 bend in the b subunit has been observed near the surface of the
 membrane (136). Shortening the b subunit by 11 amino acids (left panel) or
 lengthing by 14 amino acids(right panel) may be accompanied by the
 straightening or further bending, respectively, of this 200 bend. Genetic
 fusion proteins on the a subunit have been described by Cipriano et al.
 (represented by the yellow oval) (100). The larger the fusion protein, the
 greater the inhibition of activity due to the inability of the central stalk to
 rotate during catalysis. We propose a model in which F1Fo ATP synthase
 complexes incorporated with shorten or lengthened b subunits may
 accommodate smaller or larger fusion proteins, respectively.

the shortened b subunit, inhibition of growth might become apparent with the smaller

fusion proteins (Figure 6-2). Conversely, in complexes incorporated with the lengthened

b subunit, the tether region may bend further, allowing the larger fusion proteins to pass

between the central and peripheral stalks. Comparison of the growth properties of the

two extreme tolerable lengths of the b subunit could lend support to the flexible stalk

model .

 Other Implications

 How does the work presented in this dissertation affect the way in which the b

subunit homologues of F1Fo ATP synthase are currently viewed? This work suggests that

the importance of the b subunit dimer may be reflected in the fact that higher organisms