Evidence that C-terminal non-kinase domain of Pbs2p has a role in high osmolarity-induced nuclear localization of Hog1p.

Mitogen-activated protein kinase (MAPK) cascade is a ubiquitous signaling module that transmits extracellular stimuli through the cytoplasm to the nucleus. In baker's yeast external high osmolarity activates high osmolarity glycerol (HOG) MAPK pathway which consists of two upstream branches (SHO1 and SLN1) and common downstream elements Pbs2p MAPKK and Hog1p MAPK. Activation of this pathway causes rapid nuclear accumulation of Hog1p, essentially leading to the expression of target genes. Previously we have isolated a PBS2 homologue (DPBS2) from osmo-tolerant and salt-tolerant yeast Debaryomyces hansenii that partially complemented pbs2 mutation in Saccharomyces cerevisiae. Here we show that by replacing C-terminal region of Dpbs2p with the homologous region of Pbs2p we could abrogate partial complementation exhibited by Dpbs2p and this was achieved due to increase in nuclear translocation of Hog1p. Thus, our result showed that in HOG pathway, MAPKK has important role in nuclear translocation of Hog1p.

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