A novel yeast gene, RHK1, is involved in the synthesis of the cell wall receptor for the HM-1 killer toxin that inhibits beta-1,3-glucan synthesis

The HM-1 killer toxin from Hansenula mrakii is known to inhibit cell wall beta-1,3-glucan synthase of Saccharomyces cerevisiae and other sensitive strains of yeast. A number of mutants of Saccharomyces cerevisiae that show resistance to this toxin were isolated in order to clarify the killing mechanism of the toxin. These mutants, designated rhk (resistant to Hansenula killer), were classified into three complementation groups. A novel gene RHK1, which complements the killer-resistant phenotype of the largest complementation group rhk-1, was isolated. DNA sequence analysis revealed an open reading frame that encodes a hydrophobic protein composed of 458 amino acids. Gene disruption followed by tetrad analysis showed that RHK1 is not essential and loss of RHK1 function endowed S. cerevisiae cells with complete killer resistance. A biochemical analysis suggested that RHK1 does not participate directly in the synthesis of beta-1,3-glucan but is involved in the synthesis of the receptor for the HM-1 killer toxin.