Nuclear Import of Spo12p, a Protein Essential for Meiosis

Abstract

In Saccharomyces cerevisiae, Spo12p is involved in mitosis and is essential for meiosis. We found that Spo12p is imported into the nucleus by the karyopherin Kap121p. A complex containing Spo12p and Kap121p was isolated from cytosol and was also reconstituted with recombinant proteins, indicating that this interaction is direct. Spo12p was mislocalized to the cytosol in pse1-1, a temperature-sensitive strain harboring a mutation of Kap121p, at the permissive temperature, confirming an essential role for Kap121p in Spo12p import. Spo12p was also mislocalized in a pse1-1/pse1-1 homozygous strain, suggesting it is imported via the same pathway in diploid cells. Furthermore, we found that pse1-1/pse1-1 shows a sporulation defect similar to that of spo12Delta/spo12Delta. In addition, we have characterized the Spo12p nuclear localization signal, mapped it to residues 76-130, and identified residues within this region that are important for nuclear localization signal function.