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Mol. Cell. Biol., Aug 1996, 4095-4106, Vol 16, No. 8
DM Lyons, SK Mahanty, KY Choi, M Manandhar and EA Elion
The mating mitogen-activated protein kinase (MAPK) cascade has three major
outputs prior to fusion: transcriptional activation of many genes, cell
cycle arrest in the G1 phase, and polarized growth. Bem1 localizes near the
cortical actin cytoskeleton and is essential for polarized growth during
mating. Here we show that Bem1 is required for efficient signal
transduction and coordinates MAPK cascade activation with G1 arrest and
mating. bem1delta null mutants are defective in G1 arrest and
transcriptional activation in response to mating pheromone. Bem1 protein
stimulates Fus3 (MAPK) activity and associates with Ste5, the tethering
protein essential for activation of the MAPK kinase kinase Ste11. Bem1-Ste5
complexes also contain Ste11, Ste7 (MAPK kinase), and Fus3, suggesting that
Ste5 localizes the MAPK cascade to Bem1. Strikingly, Bem1 also copurifies
with Far1, a Fus3 substrate required for G1 arrest and proper polarized
growth during mating. These and other results suggest that Bem1 may
cross-link the Ste5-MAPK cascade complex to upstream activators and
specific downstream substrates at the shmoo tip, thus enabling efficient
circuitry for G1 arrest and mating.
Copyright © 1996, American Society for Microbiology
The SH3-domain protein Bem1 coordinates mitogen-activated protein kinase cascade activation with cell cycle control in Saccharomyces cerevisiae
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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