Increased chitin synthesis in response to type II myosin deficiency in Saccharomyces cerevisiae

We reported previously that the chitin content in cell walls of type II myosin-deficient Saccharomyces cerevisiae strains is increased relative to wild-type cells suggesting that increased chitin synthesis is induced in these strains. In the present study, we have performed enzyme activity assays for chitin synthases 1, 2, and 3 to determine the enzyme isoform(s) involved. To determine if transcriptional regulation is involved, we conducted quantitative mRNA assays of the corresponding chitin synthase genes. We show that the enzyme activities of all three chitin synthases increase substantially over the wild-type strain while eight- and twofold increases in the mRNA levels for chitin synthases 1 and 3 were detected. Increases in enzyme activities and mRNA levels were not proportional. We conclude that the enzyme activities for all three chitin synthases are elevated in this strain and that this increase is mediated mainly by a posttranslational mechanism(s). The heightened sensitivity to osmotic stress and the corresponding increase in cell wall chitin content reported in these strains are consistent with a compensatory "stress response" mechanism induced by abnormal cell wall assembly.