Journal of Bacteriology, September 2000, p. 4752-4757, Vol. 182, No. 17
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Departamento de Microbiologia y Genética/Instituto de Microbiologia Bioquimica, Universidad de Salamanca/CSIC, Campus Miguel de Unamuno, 37007 Salamanca, Spain,1 and Dipartimento di Fisiologia e Biochimica Generali, Università degli Studi di Milano, 20133 Milano, Italy2
Received 20 March 2000/Accepted 6 June 2000
The existence of a compensatory mechanism in response to cell wall
damage has been proposed in yeast cells. The increase of chitin
accumulation is part of this response. In order to study the mechanism
of the stress-related chitin synthesis, we tested chitin synthase I
(CSI), CSII, and CSIII in vitro activities in the cell-wall-defective
mutant gas1
. CSI activity increased twofold with respect
to the control, a finding in agreement with an increase in the
expression of the CHS1 gene. However, deletion of the
CHS1 gene did not affect the phenotype of the
gas1
mutant and only slightly reduced the chitin
content. Interestingly, in chs1 gas1 double mutants the
lysed-bud phenotype, typical of chs1 null mutant, was
suppressed, although in gas1 cells there was no reduction in chitinase activity. CHS3 expression was not affected in
the gas1 mutant. Deletion of the CHS3 gene
severely compromised the phenotype of gas1 cells, despite
the fact that CSIII activity, assayed in membrane fractions, did not
change. Furthermore, in chs3 gas1 cells the chitin level
was about 10% that of gas1 cells. Thus, CSIII is the
enzyme responsible for the hyperaccumulation of chitin in response to
cell wall stress. However, the level of enzyme or the in vitro CSIII
activity does not change. This result suggests that an interaction with
a regulatory molecule or a posttranslational modification, which is not
preserved during membrane fractionation, could be essential in vivo for
the stress-induced synthesis of chitin.
Present address: Università degli Studi di Milano-Bicocca,
Dipartimento di Biotecnologie e Bioscienze, 20126 Milano, Italy.
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