Summary: Previous results [E. Cabib, A. Sburlati, B. Bowers & S. J. Silverman (1989) 108, 1665-1672] strongly suggested that the lysis observed in daughter cells of defective in chitin synthase 1 (Chs1) was caused by a chitinase that partially degrades the chitin septum in the process of cell separation. Consequently, it was proposed that in wild-type cells, Chs1 acts as a repair enzyme by replenishing chitin during cytokinesis. The chitinase requirement for lysis has been confirmed in two different ways: () demethylallosamidin, a more powerful chitinase inhibitor than the previously used allosamidin, is also a much better protector against lysis and () disruption of the chitinase gene in cells eliminates lysis. Reintroduction of a normal chitinase gene, by transformation of those cells with a suitable plasmid, restores lysis. The percentage of lysed cells in strains lacking Chs1 was not increased by elevating the chitinase level with high-copy-number plasmids carrying the hydrolase gene. Furthermore, the degree of lysis varied in different strains; lysis was abolished in mutants containing the suppressor. These results indicate that, in addition to chitinase, lysis requires other gene products that may become limiting.


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