Haploid yeast cells are able to
invade agar when grown on rich media. This phenotype appears
manifestly in cells of the Sigma1278b genetic background. Diploid
cells on the nitrogen-poor agar media develop pseudohyphae
formation. Invasion and pseudohyphae formation is regulated by
KSS1 MAPK pathway and cAMP-regulated pathway. The KEM1
gene has been reported to affect microtubule and spindle pole body
(SPB) functions during conjugation and mitotic cell growth. The
kem1 mutations cause a bilateral nuclear fusion defect, benomyl
hypersensitivity, and a delay in SPB separation. Diverse functions
have been suggested for the Kem1 protein such as a
microtubule-associated protein or cytoplasmic exoribonuclease. We
observed that KEM1 affects the pheromone-mediated induction of
karyogamy-specific gene, KAR3 and KAR4. This regulation
appears to be at the post-transcription level. Here we report the
KEM1 is also involved in both invasive growth and pseudohyphae
formation. The disruption of the KEM1 gene in the Sigma1278b
background significantly reduces invasive growth and pseudohyphal
growth. The kem1 mutation causes the reduced expression of
FLO11 that encodes a cell wall protein that is required for
both invasion and pseudohyphal formation. These results imply that
KEM1 is required for invasive growth and pseudohyphae formation
by the regulation of FLO11. We are currently investigating the
relationship between KEM1 and KSS1 MAPK components.
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