Functional characterization of the fission yeast Start-specific transcription factor Res2.

In the fission yeast Schizosaccharomyces pombe, transcriptional activation at Start is mediated by complexes that bind the MCB. Two such complexes have been identified; both contain the Cdc10 protein in partnership with either the Res1 or Res2 protein. Characterization of null mutants suggests that the Res1-Cdc10 complex predominantly functions in mitotic cells whereas the Res2-Cdc10 complex is required for meiosis and spore formation. Here we have characterized the functional domains of the Res2 protein. The N-terminus is both necessary and sufficient for DNA binding, whereas the C-terminus is the region involved in the interaction with the Cdc10 protein. The centrally located ankyrin repeats are dispensable for both functions. Res2 binds to DNA as a dimer. In addition, complexes containing both Res1 and Res2 can form and bind to DNA in vitro. Furthermore, the major MCB-specific complex detected in extracts from wild-type cells contains Res1 and Res2; the complex is lost when either gene is deleted and can be recognized by antibodies specific to both proteins. In order to understand the basis for the specific function of Res2 in meiosis, hybrids between Res1 and Res2 were constructed and their functions analysed. The results indicate an absolute requirement for the Res2 C-terminus for normal meiosis to occur whereas the origin of the DNA-binding region is irrelevant. The implications of these results for the regulation of the MCB-binding complexes will be discussed.