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GAS2 and GAS4, a Pair of Developmentally Regulated Genes Required for Spore Wall Assembly in Saccharomyces cerevisiae

Enrico Ragni,¹ Alison Coluccio,² Eleonora Rolli,¹ José Manuel Rodriguez-Peña,³ Gaia Colasante,^1, Javier Arroyo,³ Aaron M. Neiman,² and Laura Popolo^1*

Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, 20133 Milano, Italy,¹ Department of Biochemistry and Cell Biology, SUNY Stony Brook, Stony Brook, New York 11794-5215,² Departamento de Microbiología II, Universidad Complutense de Madrid, CP 28040 Madrid, Spain³

Received 9 October 2006/ Accepted 15 December 2006

The GAS multigene family of Saccharomyces cerevisiae is composed of five paralogs (GAS1 to GAS5). GAS1 is the only one of these genes that has been characterized to date. It encodes a glycosylphosphatidylinositol-anchored protein functioning as a ß(1,3)-glucan elongase and required for proper cell wall assembly during vegetative growth. In this study, we characterize the roles of the GAS2 and GAS4 genes. These genes are expressed exclusively during sporulation. Their mRNA levels showed a peak at 7 h from induction of sporulation and then decreased. Gas2 and Gas4 proteins were detected and reached maximum levels between 8 and 10 h from induction of sporulation, a time roughly coincident with spore wall assembly. The double null gas2 gas4 diploid mutant showed a severe reduction in the efficiency of sporulation, an increased permeability of the spores to exogenous substances, and production of inviable spores, whereas the single gas2 and gas4 null diploids were similar to the parental strain. An analysis of spore ultrastructure indicated that the loss of Gas2 and Gas4 proteins affected the proper attachment of the glucan to the chitosan layer, probably as a consequence of the lack of coherence of the glucan layer. The ectopic expression of GAS2 and GAS4 genes in a gas1 null mutant revealed that these proteins are redundant versions of Gas1p specialized to function in a compartment at a pH value close to neutral.

Published ahead of print on 22 December 2006.

Present address: DIBIT, San Raffaele Scientific Institute, Via Olgettina 58, 20132 Milano, Italy.

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