A temperature‐sensitive mutant of the yeast plasma membrane ATPase obtained by in vitro mutagenesis

The yeast plasma membrane ATPase is a proton pump essential for cell growth. We have further analyzed the physiological role of the enzyme by constructing a temperature‐sensitive mutant. The cloned gene was treated with hydroxylamine and introduced into a haploid strain in which the constitutive promoter of the ATPase gene had been replaced by a galactose‐dependent promoter. One transformant exhibited thermosensitive growth on glucose but not on galactose. Under non‐permissive conditions the mutant is defective in proton efflux and amino acid uptake and it stops growing either unbudded or with an elongated bud. These results constitute the first genetic evidence for the chemiosmotic role of the enzyme suggested by biochemical and physiological studies.