9 Transport across Yeast Vacuolar and Plasma Membranes

Abstract

I. INTRODUCTION
The traditional approaches to transport in yeast were based on kinetic studies and on the selection of transport mutants (Cooper 1982). A later development was the application of Mitchell’s chemiosmotic hypothesis, which clarified the bioenergetic aspects of transport (Eddy 1982; Serrano 1985). During recent years, several molecular approaches have complemented the knowledge previously obtained at the cellular level. One approach is the purification of transport components. This has been most successful in the case of plasma membrane (Serrano 1988b) and vacuolar (Uchida et al. 1988a) H⁺-ATPases because of their abundance and the availability of an easy assay to follow purification. Permeases, even if abundant, require reconstitution into liposomes before their activities can be measured. Second, the introduction of recombinant DNA methodologies has provided an explosion of information on the primary structures of transport proteins. This has allowed their grouping into protein families and the development of models for their structures and mechanisms. A mutational analysis has been performed with the cloned plasma membrane H⁺-ATPase, and it has provided insights about functional domains and physiological roles of the enzyme. A similar analysis has been started with the vacuolar H⁺-ATPase. Finally, electrophysiological methodologies have provided a physical approach to ion transport at the molecular level. In particular, patch clamping has allowed the identification for the first time of ion channels in yeast.

These novel developments constitute the basis for the present chapter, which attempts to complement the review by Cooper (1982). Some classic aspects not previously covered are also briefly...