Chitin synthetase 2, a presumptive participant in septum formation in Saccharomyces cerevisiae

Abstract

Strains containing a disrupted structural gene for chitin synthetase (chs1::URA3) are defective in chitin synthetase 1 (Chs1) activity but contain normal amounts of chitin (Bulawa, C.E., Slater, M., Cabib, E., Au-Young, J., Sburlati, A., Adair, L., and Robbins, P. W. (1986) Cell 46, 213-225). We have now detected in such strains a new chitin synthetase activity (Chs2), at levels about 5% of those of Chs1 in wild-type cells. Thus, Chs2 is presumably the physiological agent for chitin deposition in strains with a disrupted CHS1 gene and probably also in wild-type strains. Chs1 and Chs2 share certain properties, such as stimulation by N-acetylglucosamine and by partial proteolysis. They differ sharply, however, in divalent cation specificity and in pH optimum. Chs2 also shows less sensitivity than Chs1 to inhibition by polyoxin D or sodium chloride, a property that was used to demonstrate the presence of Chs2 in wild-type extracts. As in the case of Chs1, most of the Chs2 activity was found to be associated with the plasma membranes. This finding, together with the apparent zymogenic nature of Chs2, is consistent with the hypothesis, previously put forward for Chs1, that localized deposition of chitin is attained by activation of the zymogen form at a specific time and place. Function and significance of the two chitin synthetases are discussed in connection with fungal morphogenesis and evolution.