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The pvp (pre-mRNA processing) mutants of the fission yeast Schizosaccharomyces pombe have a defect in pre-mRNA splicing and accumulate mRNA precursors at a restrictive temperature. One of the prp mutants, prp1-4, also has a defect in poly[(A).sup.+] RNA transport. The prp[1.sup.+] gene encodes a protein of 906 amino acid residues that contains 19 repeats of 34 amino acids termed tetratrico peptide repeat (TPR) motifs, which were proposed to mediate protein-protein interactions. The amino acid sequence of Prp1p shares 29.6% identity and 50.6% similarity with that of the PRP6 protein of Saccharomyces cerevisiae, which is a component of the U4/U6 snRNP required for spliceosome assembly. No functional complementation was observed between S. pombe prp[1.sup.+] and S. cerevisiae PRP6. We examined synthetic lethality of prp1-4 with the other known pvp mutations in S. pombe. The results suggest that Prp1p interacts either physically or functionally with Prp4p, Prp6p and Prp13p. Interestingly, the prp[1.sup.+] gene was found to be identical with the zer[1.sup.+] gene that functions in cell cycle control. These results suggest that Prp1p/Zer1p is either directly or indirectly involved in cell cycle progression and/or poly[(A).sup.+] RNA nuclear export, in addition to pre-mRNA splicing.

Transport of mRNA from the nucleus to the cytoplasm is one of the important steps in gene expression in eukaryotic cells. To elucidate a mechanism of mRNA export, we identified a novel ptr [poly[(A).sup.+] RNA transport] mutation, ptr6, which causes accumulation of mRNA in the nucleus and inhibition of growth at the nonpermissive temperature. The ptr[6.sup.+] gene was found to encode an essential protein of 393 amino acids, which shares significant homology in amino acid sequence with yTAFII67 of budding yeast Saccharomyces cerevisiae and human hTAFII55, a subunit of the general transcription factor complex TFIID. A Ptr6p-GFP fusion protein is localized in the nucleus, suggesting that Ptr6p functions there. Northern blot analysis using probes for 10 distinct mRNAs showed that the amount of [tbp.sup.+] mRNA encoding the TATA-binding protein is increased five- to sixfold, whereas amounts of others are rapidly decreased at the nonpermissive temperature in ptr6-1, ptr6 has no defects in nuclear import of an NLS-GFP fusion protein. These results suggest that Ptr6p required for mRNA transport is a Schizosaccharomyces pombe homologue of yTAFII67 and hTAFII55. This is the first report suggesting that a TAF is involved in the nucleocytoplasmic transport of mRNA in addition to the transcription of the protein-coding genes.