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


Tokio Tani1, Takashi Ideue2, Fumitaka Mizuki2, Sin Hwang2, Jun-ichi Yoshida2 and Yasumi Ohshima2
1Dept. Biol. Sci., Kumamoto Univ., Kumamoto, 860-8555, Japan, 2Dept. Biol., Kyushu Univ., Fukuoka 812-8581, Japan
@In eukaryotic cells, transport of mRNA from the nucleus to the cytoplasm is one of the essential steps in gene expression. To examine the mechanism of nucleocytoplasmic transport of mRNA, we have identified 11groups of mutants named ptr (poly A+ RNA transport) that accumulate poly A+ RNA in the nuclei at the nonpermissive temperature.
@ We have cloned and characterized each ptr+ gene. Of those, the ptr1+ and ptr3+ genes encode a ubiquitin ligase E3-like protein with the hect domain and a homologue for the ubiquitin activating enzyme E1, respectively, thereby suggesting that the ubiquitin system plays a role in mRNA export. The ptr6+ gene encodes a homologue for human TAFII55, a subunit of the general transcription factor complex TFIID. Interestingly, we also found that the product of the ptr8+ gene shares a high homology in aminoacid sequence with those of RAD25 of S. cerevisiae and human XPB/ERCC3, a component of the basal transcription factor complex TFIIH involved in gene transcription, transcription-coupled DNA excision repair, and regulation of the cell cycle progression. ptr8 accumulates mRNA in the nucleus very rapidly after shifting to the nonpermissive temperature, indicating direct involvement of Ptr8p in the process of nucleocytoplasmic transport of mRNA. In addition, the ptr7+ gene encodes a putative homologue for S. cerevisiae Clp1p, a component of CFIA essential for the 3' endprocessing. These results suggest that a functional crosstalk exists among gene transcription, 3' end processing and nuclear export ofmRNA.