REGULATION OF THE MTS1-MTS2-DEPENDENT ADE6-M26 MEIOTIC RECOMBINATION HOT-SPOT AND DEVELOPMENTAL DECISIONS BY THE SPC1 MITOGEN-ACTIVATED PROTEIN-KINASE OF FISSION YEAST

The M26 meiotic recombination hot spot in the ade6 gene of Schizosacch aromyces pombe is activated by the heterodimeric M26 binding protein M ts1-Mts2. The individual Mts1 (Atf1, Gad7) and Mts2 (Pcr1) proteins ar e also transcription factors involved in developmental decisions. We r eport that the Mts proteins are key effecters of at least two distinct classes of developmental decisions regulated by the mitogen-activated protein (MAP) kinase cascade. The first class (osmoregulation, spore viability, and spore quiescence) requires the Spc1 MAP kinase and the Mts1 protein but does not require the Mts2 protein. The second class ( mating, meiosis, and recombination hot spot activation) requires the S pc1 kinase and the Mts1-Mts2 heterodimer. Northern and Western blottin g eliminated any significant role for the Spc1 kinase in regulating th e expression levels of the Mts proteins. Gel mobility shift experiment s indicated that the Mts1-Mts2 heterodimer does not need to be phospho rylated to bind to ade6-M26 DNA in vitro. However, in vivo dimethyl su lfate footprinting demonstrated that protein-DNA interaction within ce lls is dependent upon the Spc1 MAP kinase, which phosphorylates the Mt s1 protein. Thus, the Spc1 kinase helps regulate the effector activiti es of the Mts1-Mts2 heterodimer in part by modulating its ability to o ccupy the M26 DNA site in vivo. Meiotic recombination hot spot functio n is likely the result of DNA conformational changes imparted by bindi ng of the Mts1-Mts2 meiotic transcription factor.