Expression of the AZR1 gene (ORF YGR224w), encoding a plasma membrane transporter of the major facilitator superfamily, is required for adaptation toacetic acid and resistance to azoles in Saccharomyces cerevisiae

In this work, we report results on the functional analysis of Saccharomyces cerevisiae ORF YGR224w, predicted to code for an integral membrane protein , with 14 potential transmembrane segments, belonging to the major facilita tor superfamily (MFS) of transporters which are required for multiple-drug resistance (MDR). This MFS-MDR homologue is required for yeast adaptation t o high stress imposed by low-chain organic acids, in particular by acetic a cid, and for resistance to azoles, especially to ketoconazole and fluconazo le; the encoding gene was thus named the AZR1 gene. These conclusions were based on the higher susceptibility to these compounds of an azr1 Delta dele tion mutant strain compared with the wild-type and on the increased resista nce of both azr1 Delta and wildtype strains upon increased expression of th e AZR1 gene from a centromeric plasmid clone. AZR1 gene expression reduces the duration of acetic acid-induced latency, although the growth kinetics o f adapted cells under acetic acid stress is apparently independent of AZR1 expression level. Fluorescence microscopy observation of the distribution o f the Azr1-GFP fusion protein in yeast living cells indicated that Azr1 is a plasma membrane protein. Studies carried out to gain some understanding o f how this plasma membrane putative transporter facilitates yeast adaptatio n to acetic acid did not implicate Azr1p in the alteration of acetic acid a ccumulation into the cell through the active efflux of acetate. Copyright ( C) 2000 John Wiley & Sons, Ltd.