Fission yeast ptr4-1 is one of the mRNA transport mutants that accumulate poly(A)(+) RNA in the nuclei at the nonpermissive temperature. We cloned the ptr4(+) gene and found that it is identical with the cut1(+) gene essential for chromosome segregation during mitosis. ptr4/cut1 has no defects in nucleocytoplasmic transport of a protein, indicative of a specific blockage of mRNA export by this mutation. A mutant of Cut2p cooperating with Cut1p in sister chromatid separation also showed defective mRNA export at the nonpermissive temperature. Our results suggest a novel linkage between the cell division cycle and nuclear mRNA export in eukaryotic cells.