Originally published as Genetics Published Articles Ahead of Print on June 3, 2005.

Genetics, Vol. 171, 7-21, September 2005, Copyright © 2005
doi:10.1534/genetics.105.042598

The Fission Yeast Schizosaccharomyces pombe Has Two Importin- Proteins, Imp1p and Cut15p, Which Have Common and Unique Functions in Nucleocytoplasmic Transport and Cell Cycle Progression

Makoto Umeda^*, Shahed Izaddoost^*,1, Ian Cushman^,,2, Mary Shannon Moore^,,3 and Shelley Sazer^*,,,4

^* Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030 and The Graduate Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030

⁴ Corresponding author: Department of Biochemistry and Molecular Biology, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030.
E-mail: ssazer{at}bcm.tmc.edu

The nuclear import of classical nuclear localization signal-containing proteins depends on importin- transport receptors. In budding yeast there is a single importin- gene and in higher eukaryotes there are multiple importin--like genes, but in fission yeast there are two: the previously characterized cut15 and the more recently identified imp1. Like other importin- family members, Imp1p supports nuclear protein import in vitro. In contrast to cut15, imp1 is not essential for viability, but imp1 mutant cells exhibit a telophase delay and mild temperature-sensitive lethality. Differences in the cellular functions that depend on Imp1p and Cut15p indicate that they each have unique physiological roles. They also have common roles because the imp1 and the cut15-85 temperature-sensitive mutations are synthetically lethal; overexpression of cut15 partially suppresses the temperature sensitivity, but not the mitotic delay in imp1 cells; and overexpression of imp1 partially suppresses the mitotic defect in cut15-85 cells but not the loss of viability. Both Imp1p and Cut15p are required for the efficient nuclear import of both an SV40 nuclear localization signal-containing reporter protein and the Pap1p component of the stress response MAP kinase pathway. Imp1p and Cut15p are essential for efficient nuclear protein import in S. pombe.

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