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Activation of the M26 meiotic recombination hotspot by Mts1/Mts2 protein: input from the meiotic MAP kinase cascade, site occupancy, and chromatin remodeling.

The M26 meiotic recombination hotspot in the ade6 gene of Schizosaccharomyces pombe requires a discrete nucleotide sequence (5'-ATGACGT-3'), a second inferred cis -linked DNA site, and the heterodimeric M26 binding protein Mts1/Mts2. The individual Mts1 (Atf1, Gad7) and Mts2 (Pcr1) proteins are also transcription factors with roles in a variety of developmental decisions, including meiotic entry. Genetic analyses revealed that mating, meiosis, and hotspot activation require the simultaneous presence of Mts1, Mts2, and Spc1 MAP kinase. This suggests that Mts1/Mts2 heterodimer is a key, multifunctional effector of meiotic development dependent upon the MAP kinase cascade. In vivo DMS footprinting revealed constitutive M26 site occupancy by Mts1/Mts2 protein and this site occupancy was dependent upon Spc1. During meiosis, DNA within chromatin bearing the hotspot became more sensitive to micrococcal nuclease digestion, pronounced hypersensitive sites were induced in the promoter region and at the M26 site, and nucleosomes were displaced in the vicinity of the hotspot. These changes were strictly dependent upon meiosis, the M26 site, and the Mts1/Mts2 heterodimer, demonstrating an essential role for Mts1/Mts2 protein in meiotic chromatin remodeling. We propose a model of hotspot activation involving the assembly of binary, ternary, and quaternary complexes that remodel chromatin during recruitment of meiotic recombination enzymes.

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