Nuclear roles and regulation of chromatin structure by the stress-dependent MAP kinase Sty1 of Schizosaccharomyces pombe.

Microorganisms are invariably exposed to abrupt changes in their environment, and consequently display robust, high plasticity gene programmes to respond to stresses. In fission yeast, the Sty1 pathway is activated in response to diverse stress conditions, such as osmotic and oxidative stress, heat shock or nitrogen deprivation. The MAP kinase Sty1 and its substrate, the transcription factor Atf1, regulate diverse processes mainly at the nucleus. For instance, Sty1, Atf1 and its heterodimeric partner Pcr1 participate in promoting recombination at some hot spots, and in the assembly of heterochromatin at the mating locus. Their main role, however, is to engage a wide gene expression programme aimed to allow cellular survival by decreasing and repairing the damage exerted. Once Sty1 and Atf1 are activated by stress, they are recruited to promoters of up to 5-10% of the coding genes and regulate their transcription. Even though there is no simple, global relationship establishing RNA polymerase II occupancy, nucleosome architecture and transcriptional activity in eukaryotes, we discuss within this review the current knowledge and future perspectives of how activation of Sty1 and Atf1 affect chromatin architecture of a large fraction of the Schizosaccharomyces pombe genome to trigger the cellular response to environmental stress.