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First published online 16 June 2005
doi: 10.1242/jcs.02418

This Article Figures Only Full Text Full Text (PDF) Supplementary Material A correction has been published All Versions of this Article: jcs.02418v1 118/13/2837    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Qi, M. Articles by Elion, E. A. Search for Related Content PubMed PubMed Citation Articles by Qi, M. Articles by Elion, E. A.

Formin-induced actin cables are required for polarized recruitment of the Ste5 scaffold and high level activation of MAPK Fus3

Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, MA 02115, USA

^* Author for correspondence (e-mail: elaine_elion{at}hms.harvard.edu)

Accepted 5 April 2005

Little is known about how a mitogen-activated protein kinase (MAPK) cascade is targeted to specific sites at the plasma membrane during receptor stimulation. In budding yeast, the Ste5 scaffold is recruited to a receptor-coupled G protein during mating pheromone stimulation, allowing the tethered MAPK cascade to be activated by Ste20, a Cdc42-anchored kinase. Here we show that stable recruitment of Ste5 at cortical sites requires the formin Bni1, Bni1-induced actin cables, Rho1 and Myo2. Rho1 directs recruitment of Bni1 via the Rho-binding domain, and Bni1 mediates localization of Ste5 through actin cables and Myo2, which co-immunoprecipitates with Ste5 during receptor stimulation. Bni1 is also required for polarized recruitment and full activation of MAPK Fus3, which must bind Ste5 to be activated, and polarized recruitment of Cdc24, the guanine exchange factor that binds Ste5 and promotes its recruitment to the G protein. In contrast, Bni1 is not important for activation of MAPK Kss1, which can be activated while not bound to Ste5 and does not accumulate at cortical sites. These findings reveal that Bni1 mediates the formation of a Ste5 scaffold/Fus3 MAPK signaling complex at polarized sites, and suggests that a pool of Ste5 may translocate along formin-induced actin cables to the cell cortex.

Key words: Ste5 scaffold, MAPK, Formin, Bni1, Actin cytoskeleton, Polarization

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