A SMALL PROTEIN (AGS1P) AND THE PHO80P-PHO85P KINASE COMPLEX CONTRIBUTE TO AMINOGLYCOSIDE ANTIBIOTIC-RESISTANCE OF THE YEAST SACCHAROMYCES-CEREVISIAE

We identified the AGS1 and AGS3 genes by their ability to partially co mplement an ags mutant (RC1707) which is supersensitive to various ami noglycoside antibiotics (J. F. Ernst and R. K. Chan, J. Bacteriol, 163 :8-14, 1985). AGS1 is located in proximity to the centromere of chromo some III and encodes a small protein of 88 amino acids. The size of th e AGS1 transcript, which in wild-type cells is I kb, is reduced to 0.7 5 kb in mutant RC1707. Disruption of AGS1 rendered strains supersensit ive to hygromycin B and increased their resistance to vanadate. In add ition, ags1 Delta strains underglycosylated invertase but had normal c arboxypeptidase Y glycosylation, suggesting that Ags1p is required for the elaboration of outer N-glycosyl chains. AGS3 was found to be iden tical to PHO80 (TUP7), which encodes a cyclin activating the Pho85p pr otein kinase. Deletion of either PHO80 or PBO85 led to aminoglycoside supersensitivity; pho80 Delta ags1 Delta strains showed an enhanced-se nsitivity phenotype compared to single mutants. pho80 and pho85 mutant s were rendered resistant by deletion of PHO4, indicating that activat ion of the Pho4p transcription factor is required for increased aminog lycoside sensitivity. Thus, both the Pho80p-Pho85p kinase complex (by Pho4p phosphorylation) and a novel component of the N glycosylation pa thway contribute to basal levels of aminoglycoside resistance in Sacch aromyces cerevisiae.