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Eukaryotic Cell, October 2003, p. 949-961, Vol. 2, No. 5
1535-9778/03/$08.00+0     DOI: 10.1128/EC.2.5.949-961.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Phosphorylation of the MAPKKK Regulator Ste50p in Saccharomyces cerevisiae: a Casein Kinase I Phosphorylation Site Is Required for Proper Mating Function¹

Cunle Wu,^1* Mathieu Arcand,² Gregor Jansen,^1,3 Mei Zhong,^1, Tatiana Iouk,^1,3 David Y. Thomas,^1,3 Sylvain Meloche,² and Malcolm Whiteway^1,4

Genetics Group, Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec, Canada H4P 2R2,¹ Institut de Recherches Cliniques de Montréal and Department of Pharmacology, Université de Montréal, Montreal, Quebec, Canada H2W 1R7,² Department of Biochemistry, McGill University, Montreal, Quebec, Canada H3G 1Y6,³ Department of Biology, McGill University, Montreal, Quebec, Canada H3A 1B1⁴

Received 23 July 2003/ Accepted 26 July 2003

The Ste50 protein of Saccharomyces cerevisiae is a regulator of the Ste11p protein kinase. Ste11p is a member of the MAP3K (or MEKK) family, which is conserved from yeast to mammals. Ste50p is involved in all the signaling pathways that require Ste11p function, yet little is known about the regulation of Ste50p itself. Here, we show that Ste50p is phosphorylated on multiple serine/threonine residues in vivo. Threonine 42 (T42) is phosphorylated both in vivo and in vitro, and the protein kinase responsible has been identified as casein kinase I. Replacement of T42 with alanine (T42A) compromises Ste50p function. This mutation abolishes the ability of overexpressed Ste50p to suppress either the mating defect of a ste20 ste50 deletion mutant or the mating defect of a strain with a Ste11p deleted from its sterile-alpha motif domain. Replacement of T42 with a phosphorylation-mimetic aspartic acid residue (T42D) permits wild-type function in all assays of Ste50p function. These results suggest that phosphorylation of T42 of Ste50p is required for proper signaling in the mating response. However, this phosphorylation does not seem to have a detectable role in modulating the high-osmolarity glycerol synthesis pathway.

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* Corresponding author. Mailing address: Genetics Group, Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Ave., Montreal, Quebec, Canada H4P 2R2. Phone: (514) 496-6202. Fax: (514) 496-6213. E-mail: cunle.wu{at}cnrc-nrc.gc.ca.

¹ This is publication number 46158 of the National Research Council of Canada.

Present address: CuraGen Corporation, 20 Commercial St., Branford, CT 06405.

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Eukaryotic Cell, October 2003, p. 949-961, Vol. 2, No. 5
1535-9778/03/$08.00+0     DOI: 10.1128/EC.2.5.949-961.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Hao, N., Zeng, Y., Elston, T. C., Dohlman, H. G. (2008). Control of MAPK Specificity by Feedback Phosphorylation of Shared Adaptor Protein Ste50. J. Biol. Chem. 283: 33798-33802 [Abstract] [Full Text]  
• Wu, C., Jansen, G., Zhang, J., Thomas, D. Y., Whiteway, M. (2006). Adaptor protein Ste50p links the Ste11p MEKK to the HOG pathway through plasma membrane association.. Genes Dev. 20: 734-746 [Abstract] [Full Text]