Research‚Φ–ί‚ι

Cold spring harber meeting "Dynamic Organization of nuclear function"@(2002”N9ŒŽACold spring harbor, Cold spring harbor laboratory)
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UNEQUAL DISTRIBUTION OF THE NUCLEOLUS AFTER THE CELL DIVISION RESULTS IN NUCLEAR ACCUMULATION OF POLY(A)+ mRNA IN FISSION YEAST
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Takashi Ideue1, Abul Kalam Azad1*, Tadao Matsusaka2, Mitsuhiro Yanagida3. Yasumi Ohshima1and Tokio Tani4
1Dept. Biol., Kyushu Univ., Fukuoka, Japan, 2Dept. Env. Sci., Kumamoto Univ., Kumamoto, Japan, 3Dept. Biophysics, Kyoto Univ., Kyoto, Japan, 4Dept. Biol. Sci., Kumamoto Univ., Kumamoto, Japan.
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@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 eleven temperature sensitive mutants defective in mRNA export at the nonpermissive temperature in Schizosaccharomyces pombe (ptr1~11; poly(A)+ RNA transport).
@Of those, ptr4 and ptr11 exhibited the cut (cell untimely torn) phenotype, in which the cytokinesis occurs without prior nuclear division, in addition to the mRNA export defects at the nonpermissive temperature. We have cloned the ptr4+ and ptr11+ genes and found that those genes are identical with the cut1+ and top2+ genes, respectively, the mutants of which were also known to show the cut phenotype at the nonpermissive temperature. To investigate a relation between the defect in mRNA export and the cut phenotype, 14 S. pombe mutants exhibiting the cut phenotype at the nonpermissive temperature were subjected to in situ hybridization with the oligo dT probe. As a result, we found that all the tested mutants with the cut phenotype accumulate poly(A)+ RNA in the nuclei at the nonpermissive temperature. Interestingly, poly(A)+ RNA was accumulated in only one side of the cleaved nuclei in those mutants. Immunostaining with anti-fibrillarin antibody revealed that poly(A)+ RNA was always accumulated in the cleaved nucleus without the nucleolus, and mRNA export in the other half of the cleaved nucleus containing the nucleolus seemed to be normal, suggesting that presence of the nucleolus is prerequisite for mRNA export in yeast. Furthermore, we found that the mutants displaying abnormal nucleolar structure, such as nuc1 or top1 top2 double mutants, accumulate mRNA in the nucleus at the nonpermissive temperature. These results suggested that the yeast nucleolus might play a role not only in rRNA synthesis and pre-ribosome assembly but also in mRNA export.
*Present address: Sir William Dunn School of Pathology, University of Oxford