Chitin synthase I and chitin synthase II are not required for chitin synthesis in vivo in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, the polysaccharide chitin forms the primary division septum between mother cell and bud. Two related enzymes, chitin synthase I and chitin synthase II (UDP-acetamido-2-deoxy-D-glucose:chitin 4-β-acetamidodeoxyglucosyltransferase, EC 2.4.1.16), have been identified and their structural genes, CHS1 and CHS2, respectively, have been cloned and sequenced. Gene disruption experiments led to the conclusion that CHS2 is essential for cell division [Silverman, S. J., Sburlati, A., Slater, M. L. \& Cabib, E. (1988) Proc. Natl. Acad. Sci. USA 85, 4735-4739], whereas CHS1 is not. We repeated the disruption of CHS2 and determined that it is not essential for vegetative growth. The viability of chs1::HIS3 chs2::TRP1 spores is influenced by strain background and germination conditions. The double disruption mutant has no detectable chitin deficiency in vivo, as judged by quantitative assay and by staining cells with Calcofluor. Assay of membrane preparations from the double disruption mutant indicates the presence of chitin synthetic activity. Unlike the CHS gene products, this third activity is not stimulated by trypsin. Characterization of the double disruption mutant revealed abnormalities in morphology and nuclear migration.