Saccharomyces cerevisiae osmotic fragile mutants were obtained from parental strain SH208 15 by N methyl N’ nitro N nitrosoguanidine(NTG) treatments. Three mutants, HF2, HF7 and HF9 showed high degree of release of the intracellular components into medium under hypo osmotic condition and were studied in details. They showed some similar phenotypes to the previously reported fragile mutants, including hypo osmolarity sensitivity, temperature sensitivity and sensitivity to zymolyase indicating the existence of cell wall integrity defect. However, the three mutants differ from the reported mutants in some respects. Firstly, The temperature sensitivity of the isolated three mutants could not be complemented by osmotic stabilizer, while that of the PKC1 pathway mutants could be restored. Secondly, the degree of glycosylation of invertase in HF2, HF7 and HF9 did not decrease as that of srb1/vig9 mutants when compared with invertase in wild type strain respectively. In addition, the three mutants differ from each other. Hence, the three mutants are putative novel fragile mutants defect in cell wall. They can be used to further study the metabolism of yeast cell wall in biochemical and genetic levels and have the potential value to release intracellular heterologous proteins in high yield.
