Nuclear Import of Spo12p, a Protein Essential for Meiosis*

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 inpse1–1, 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/pse1–1homozygous strain, suggesting it is imported via the same pathway in diploid cells. Furthermore, we found that pse1–1/pse1–1shows a sporulation defect similar to that ofspo12Δ/spo12Δ.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.