RANDOM MUTANT GENERATION AND ITS UTILITY IN UNCOVERING STRUCTURAL ANDFUNCTIONAL FEATURES OF CYTOCHROME-B IN SACCHAROMYCES-CEREVISIAE

The generation of random mutations in the mitochondrial cytochrome b g ene of Saccharomyces cerevisiae has been used as a most fruitful means of identifying subregions that play a key role in the bc1 complex mec hanism, best explained by the protonmotive Q cycle originally proposed by Peter Mitchell. Selection for center i and center o inhibitor resi stance mutants, in particular, has yielded much information. The combi ned approaches of genetics and structural predictions have led to a tw o-dimensional folding model for cytochrome b that is most compatible w ith current knowledge of the protonmotive Q cycle. A three-dimensional model is emerging from studies of distant reversions of deficient mut ants. Finally, interactions between cytochrome b and the other subunit s of the bc1 complex, such as the iron sulfur protein, can be affected by a single amino acid change.