To identify novel factors involved in nuclear mRNA export in Schizosaccharomyces pombe, we isolated and characterized the ptr8(+) gene, mutation of which causes nuclear accumulation of poly (A)(+) RNA. The ptr8(+) gene encodes an S. pombe homologue of human XPB, a component of TFIIH involved in nucleotide excision repair (NER) and transcription. A temperature-sensitive mutant of ptr8(+) (ptr8-1) was highly sensitive to UV irradiation, as are human XPB cells. Northern blot analysis demonstrated that the amount of total poly (A)(+) mRNAs does not decrease significantly at the nonpermissive temperature in ptr8-1 cells, whereas a pulse-labeling assay using (35)S-methionine showed that protein synthesis decreases rapidly after incubation of cells at the nonpermissive temperature, suggesting that ptr8-1 cells have a defect in nuclear mRNA export. In Saccharomyces cerevisiae, a mutation in the SSL2 gene encoding a homologue of Ptr8p also causes a block of mRNA export at the nonpermissive temperature. In addition, expression of human XPB in ptr8-1 cells rescued the ts phenotype and the mRNA export defects, suggesting that human XPB may also play a role in mRNA export. Furthermore, we revealed a functional interaction between Ptr8p and Tho2p, a component of the TREX complex involved in mRNA export. These results suggest that XPB/Ptr8p plays roles not only in NER and transcription, but also plays a conserved role in mRNA export.