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Mol. Cell. Biol., 07 1997, 3508-3519, Vol 17, No. 7
AS Sengar, NA Markley, NJ Marini and D Young
We have identified a Schizosaccharomyces pombe gene, mkh1, that encodes a
MEK kinase (MEKK) homolog. The coding region of mkh1 is contained within a
single exon encoding a 1,116-amino-acid protein. The putative catalytic
domain of Mkh1 is 54% identical to the catalytic domain of S. cerevisiae
Bck1, the most closely related protein. Deletion of mkh1 did not
significantly affect cell growth or division under standard conditions.
However, mkh1delta cell growth was inhibited by high KCl or NaCl
concentrations. mkh1delta cells required a longer time to reenter the cell
cycle after prolonged stationary-phase arrest. Also, mkh1delta cells
exhibited a round cell shape, while overexpression of Mkh1 resulted in an
elongated cell shape. mkh1delta cells exhibited a more dramatic phenotype
when grown in nutrient-limiting conditions at high temperature or in
hyperosmotic medium. In such conditions, completion of cytokinesis was
inhibited, resulting in the growth of pseudohyphal filaments with multiple
septa and nuclei. Also, mkh1delta cells were hypersensitive to
beta-glucanase treatment. Together these results suggest that Mkh1
regulates cell morphology, cell wall integrity, salt resistance, cell cycle
reentry from stationary-phase arrest, and filamentous growth in response to
stress. These phenotypes are essentially identical to those exhibited by
cells lacking Pmk1/Spm1, a recently identified mitogen-activated protein
kinase. Our evidence suggests that Pmk1/Spm1 acts downstream from Mkh1 in a
common pathway. Our results also suggest that Mkh1 and Pck2 act
independently to maintain cell wall integrity, cell morphology, and salt
resistance but act in opposition to regulate filamentous growth.
Copyright © 1997, American Society for Microbiology
Mkh1, a MEK kinase required for cell wall integrity and proper response to osmotic and temperature stress in Schizosaccharomyces pombe
Department of Medical Biochemistry, University of Calgary Health Science Centre, Alberta, Canada.
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