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

Aureobasidin A (AbA), a cyclic depsipeptide produced by Aureobasidium pullulans R106, is highly toxic to fungi including Saccharomyces cerevisiae. We isolated several dominant mutants of S. cerevisiae which are resistant to more than 25 micrograms/ml of AbA. From a genomic library of one such AUR1 mutant, the AUR1R (for aureobasidin resistant) 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-type aur1+ 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-type aur1+ is a target for AbA on the basis of following results. Firstly, cells that overexpress the wild-type aur1+ gene become resistant to AbA, just as cells with an AUR1R mutation do. Secondly, disruption of the aur1+ gene demonstrated that it is essential for growth. Thirdly, in the cells with a disrupted aur1 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.