AUR1, a novel gene conferring aureobasidin resistance onSaccharomyces cerevisiae: a study of defective morphologies in Aur1p-depleted cells

Aureobasidin A (AbA), a cyclic depsipeptide produced byAureobasidium pullulans R106, is highly toxic to fungi includingSaccharomyces cerevisiae. We isolated several dominant mutants ofS. cerevisiae which are resistant to more than 25 µg/ml of AbA. From a genomic library of one suchAUR1 mutant, theAUR1^R (foraureobasidinresistant) mutant gene was isolated as a gene that confers resistance to AbA on wild-type cells. Its nucleotide sequence showed that the predicted polypeptide is a hydrophobic protein composed of 401 amino acids, which contains several possible transmembrane domains and at least one predicted N-linked glycosylation site. Comparison of the mutant gene with the wild-typeaur1⁺ gene revealed that the substitution of Phe at position 158 by Tyr is responsible for acquisition of AbA resistance. We suggest that the gene product of the wild-typeaur1⁺ is a target for AbA on the basis of following results. Firstly, cells that overexpress the wild-typeaur1⁺ gene become resistant to AbA, just as cells with anAUR1^R mutation do. Secondly, disruption of theaur1⁺ gene demonstrated that it is essential for growth. Thirdly, in the cells with a disruptedaur1 locus, pleiotropic morphological changes including disappearance of microtubules, degradation of tubulin and abnormal deposition of chitin were observed. Some of these abnormalities are also observed when wild-type cells are treated with AbA. The abnormality in microtubules suggests that the Aur1 protein is involved in microtubule organization and stabilization.