Perturbation of the nucleus: A novel Hog1p-independent, Pkc1p-dependent consequence of hypertonic shock in yeast

Hypertonic shock of Saccharomyces cerevisiae activates the Hog1p MAP kinase cascade. In contrast, protein kinase C (Pkc1p) and the "cell integrity" MA P kinase cascade are critical for the response to hypotonic shock. We obser ved that hypertonic shock transiently relocated many, but not all, nuclear and nucleolar proteins to the cytoplasm. We hypothesized that the relocatio n of nuclear proteins was due to activation of the Hog1p kinase cascade, ye t, surprisingly, Hog1p was not required for these effects. In contrast, Pkc 1p kinase activity was required, although the Pkc1p MAP kinase cascade and several factors known to lie upstream and downstream of Pkc1p were not. Mor eover, sudden induction of a hyperactive form of Pkc1p was sufficient to re locate nuclear proteins. Taken together, these observations show that the s cope of involvement of Pkc1p in the organization of the nucleus considerabl y exceeds what has been characterized previously. The relocation of nuclear proteins is likely to account for the profound inhibition of RNA synthesis that was observed during hypertonic shock.