Protein kinases involved in mating and osmotic stress in the yeast Kluyveromyces lactis

Departamento de Genética Molecular and, Unidad de Biología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México. 04510 México D.F. Ap. Postal 70-242

^* To whom correspondence should be addressed. Email: rcoria{at}ifc.unam.mx.

	Abstract

Systematic disruption of genes encoding kinases and mitogen-activated protein kinases (MAPK) was performed in Kluyveromyces lactis haploid cells. The mutated strains were assayed by their capacity to mate and to respond to hyperosmotic stress. The KlSte11p MAPKKK was found to act in both mating and osmo-response pathways while the scaffold KlSte5p and the MAPK KlFus3p appeared to be specific for mating. The PAK KlSte20p and the kinase KlSte50p participated in both pathways. Protein-association experiments showed interaction of KlSte50p and KlSte20p with G and G respectively, the G protein subunits involved in the mating pathway. Both KlSte50p and KlSte20p also showed interaction with KlSte11p. Disruption mutants of the KlPBS2 and KlHOG1 genes of the canonical osmotic-response pathway resulted sensitive to high salt and high sorbitol but dispensable for mating. Mutations that eliminate the MAPKK KlSte7p activity had strong effect on mating and also showed sensitivity to osmotic stress. Finally, we found evidence of physical interaction between KlSte7p and KlHog1p, in addition to diminished Hog1p-phosphorylation after a hyperosmotic shock in cells lacking KlSte7p. This study reveals novel roles for components of transduction systems in yeast.