The 2nd international fission yeast meeting@(2002”N3ŒŽA‹ž“sŽs@‹ž“s‘Ϋ‰ο‹cκ)

Takashi Ideue1, Mari Kubota1, Abul Kalam Azad1, Mitsuhiro Yanagida2, Yasumi Ohshima1and Tokio Tani3.
1Dept. Biol., Kyushu Univ., Fukuoka 812-8581, Japan, 2Dept. Biophysics, Kyoto Univ., Kyoto, 606-8502, Japan, 3Dept. Biol. Sci., Kumamoto Univ., Kumamoto, 860-8555, Japan.
@In the eukaryotic cells, the domain for gene transcription (nucleus) is separated from the domain for protein synthesis (cytoplasm) by the nuclear membrane. Thus, transport of mRNA from the nucleus to the cytoplasm is one of the essential steps for the gene expression in the eukaryotic cells. To analyze a mechanism of mRNA transport, we isolated nine temperature sensitive mutants defective in mRNA export at the nonpermissive temperature in Schizosaccharomyces pombe (ptr1~9; poly(A)+ RNA transport). The gene responsible for each mutation has been cloned and characterized.
@In this study, we have screened further a bank of S. pombe ts mutants by in situ hybridization with an oligo dT probe and identified novel mRNA export mutants, ptr10 and ptr11. In addition to the defects in mRNA export, ptr11 exhibited the cut (cell untimely torn) phenotype, which the cytokinesis occurs without prior nuclear division. We found that the ptr11 mutation resides in the top2+ gene, of which the mutant was known to show the cut phenotype at the nonpermissive temperature. Interestingly, the ptr4+ gene was also found to be identical with the cut1+ gene. To investigate a relation between the defect in mRNA export and the cut phenotype, 14 mutants with the cut phenotype were subjected to in situ hybridization with the oligo dT probe. As a result, we found that all the tested mutants accumulate poly(A)+ RNA in the nuclei at the nonpermissive temperature. In those mutants, nuclear accumulation of mRNA seems to occur after appearance of the cut phenotype. In addition, nuclear import of the NLS-GFP reporter protein and leucine rich NES-dependent protein export in ptr4 and ptr11 were normal at the nonpermissive temperature. These results suggest that inability of the nuclear division affects the process of mRNA export in S. pombe.