NUCLEAR-LOCALIZATION OF THE C2H2 ZINC-FINGER PROTEIN MSN2P IS REGULATED BY STRESS AND PROTEIN-KINASE-A ACTIVITY

Msn2p and the partially redundant factor Msn4p are key regulators of s tress-responsive gene expression in Saccharomyces cerevisiae. They are required for the transcription of a number of genes coding for protei ns with stress-protective functions. Both Msn2p and Msn4p are Cys(2)Hi s(2) zinc finger proteins and bind to the stress response element (STR E). In vivo footprinting studies show that the occupation of STREs is enhanced in stressed cells and dependent on the presence of Msn2p and Msn4p. Both factors accumulate in the nucleus under stress conditions, such as heat shock, osmotic stress, carbon-source starvation, and in the presence of ethanol or sorbate. Stress-induced nuclear localizatio n was found to be rapid, reversible, and independent of protein synthe sis. Nuclear localization of Msn2p and Msn4p was shown to be correlate d inversely to cAMP levels and protein kinase A (PKA) activity. A regi on with significant homologies shared between Msn2p and Msn4p is suffi cient to confer stress-regulated localization to a SV40-NLS-GFP fusion protein. Serine to alanine or aspartate substitutions in a conserved PKA consensus site abolished cAMP-driven nuclear export and cytoplasmi c localization in unstressed cells. We propose stress and cAMP-regulat ed intracellular localization of Msn2p to be a key step in STRE-depend ent transcription and in the general stress response.