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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.

Chitin Synthesis in a gas1 Mutant of Saccharomyces cerevisiae

M-Henar Valdivieso,1 Laura Ferrario,2 Marina Vai,2,dagger Angel Duran,1 and Laura Popolo2,*

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 gas1Delta . 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 gas1Delta 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.

* Corresponding author. Mailing address: Università degli Studi di Milano, Dipartimento di Fisiologia e Biochimica Generali, Via Celoria 26, 20133 Milano, Italy. Phone: 39(02)70644808. Fax: 39(02)70632811. E-mail: Laura.Popolo{at}unimi.it.

dagger Present address: Università degli Studi di Milano-Bicocca, Dipartimento di Biotecnologie e Bioscienze, 20126 Milano, Italy.

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.


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