Novel WD-Repeat Protein Mip1p Facilitates Function of the Meiotic Regulator Mei2p in Fission Yeast

Abstract

In fission yeast, the onset of meiosis is triggered by activation of the RNA-binding protein Mei2p. We screened for a high-copy-number suppressor of the ectopic meiosis induced by expression of an active form of Mei2p. Consequently we isolated a truncated form of a novel gene, named mip1, from a fission yeast genomic library. Themip1 gene encoded a protein of 1,313 amino acids which carried a WD-repeat motif in the C-terminal region and was apparently conserved among eukaryotes. Mip1p was cytoplasmic, and two-hybrid and immunoprecipitation analyses demonstrated that Mip1p was bound to Mei2p in vivo. Genetic evidence indicated that wild-type Mip1p was required for the function of Mei2p to induce meiosis and that the truncated form of it (Mip1-15p) dominantly interfered with Mei2p. Mip1p appeared to be involved also in conjugation, associating with Ste11p, which is a key transcription factor for sexual development. Furthermore, Mip1p was essential for cell growth, to which neither Mei2p nor Ste11p is relevant. These results suggest that Mip1p assists functional expression of a number of proteins required for proliferation and sexual development in fission yeast.

ACKNOWLEDGMENTS

We thank K. Gull for providing the Tat1 antitubulin antibody, S. J. Elledge for providing the yeast two-hybrid system, and M. Sato for construction of some plasmids.

This work was supported by Grants-in-Aid for Scientific Research on Priority Areas (A) and for Specially Promoted Research from the Ministry of Education, Science, Sports and Culture of Japan and by the Mitsubishi Foundation. S.S.-Y. was a recipient of a JSPS Fellowship for Japanese Junior Scientist.