CELL-WALL SYNTHESIS SPECIFIC CYTOCIDAL EFFECT OF HANSENULA-MRAKII TOXIN-1 ON SACCHAROMYCES-CEREVISIAE

HM-1 toxin produced by Hansenula mrakii kills sensitive Saccharomyces cerevisiae. We found that the budding cells and the cells that respond ed to mating factor were sensitive to HM-1 toxin. These findings indic ate that the target sites of HM-1 toxin are developing buds and conjug ating tubes. The in vitro activity of beta-1,3-glucan synthase solubil ized and partially purified from S. cerevisiae membranes was inhibited by HM-1 toxin at a concentration (around 50 nM, 0.5 mu g/ml) that coi ncided well with its minimum inhibitory concentration for the growth o f yeast cells. These data indicate that the HIM-1 toxin perturbs the s ynthesis of yeast cell walls by inhibiting the glucan synthesis occurr ing at a budding site or a conjugating tube, which results in cell lys is.