EC Accepts, published online ahead of print on 22 May 2009

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Eukaryotic Cell doi:10.1128/EC.00095-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A protein phosphatase type 1-interacting protein Ysw1 is involved in proper septin organization and prospore membrane formation during sporulation

Makoto Ishihara, Yasuyuki Suda, Ichiro Inoue, Takayuki Tanaka, Tetsuo Takahashi, Xiao-Dong Gao, Yasuhisa Fukui, Sayoko Ihara, Aaron M. Neiman, and Hiroyuki Tachikawa^*

Laboratory of Biological Chemistry, Graduate School of Agricultural and Life Science, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan; Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York 11794-5215; Department of Applied Biochemistry, School of Engineering, Tokai University, Kitakaname 1117, Hiratsuka, Kanagawa 259-1292, Japan; Graduate School of Advanced Life Science, Frontier Research Center for Post-Genomic Science and Technology, Hokkaido University, N21, W11, Kita-Ku, Sapporo 001-0021, Japan

^* To whom correspondence should be addressed. Email: atachi{at}mail.ecc.u-tokyo.ac.jp.

Sporulation of Saccharomyces cerevisiae is a developmental process in which four haploid spores are generated inside a diploid cell. Gip1, a sporulation-specific targeting subunit of protein phosphatase type 1, together with its catalytic subunit, Glc7, co-localizes with septins along the extending prospore membrane, and is required for septin organization and spore wall formation. However, the mechanism, by which Gip1-Glc7 phosphatase promotes these events, is currently unclear. Here we show that Ysw1, a sporulation-specific coiled-coil protein, has a functional relationship to Gip1-Glc7 phosphatase. Over-expression of YSW1 partially suppresses the sporulation defect of a temperature-sensitive allele of gip1. Ysw1 interacts with Gip1 in a two-hybrid assay and this interaction is required for suppression. Ysw1 tagged with Green Fluorescent Protein co-localizes with septins and Gip1 along the extending prospore membrane during spore formation. Sporulation is partially defective in ysw1 mutant, and cytological analysis revealed that septin structures are perturbed and prospore membrane extension is aberrant in ysw1 cells. These results suggest that Ysw1 functions with the Gip1-Glc7 phosphatase to promote proper septin organization and prospore membrane formation.