The 2nd international fission yeast meeting@(2002N3Ass@sΫοcκ)
Ptr7p, A NOVEL ATP/ADP BINDING PROTEIN, IS REQUIRED FOR BIDIRECTIONAL
TRANSPORT OF MACROMOLECULES BETWEEN THE NUCLEUS AND CYTOPLASM
|Asako Shigematsu1, Jun-ichi Yoshida1,2,
Yasumi Ohshima1 and Tokio Tani2
1Dept. Biol., Kyushu Univ., Fukuoka 812-8581, Japan, 2Dept. Biol. Sci., Kumamoto Univ., Kumamoto, 860-8555, Japan.
| @Export of mature mRNA from the nucleus to the cytoplasm
is essential for the gene expression in eukaryotic cells. To elucidate
the mechanism of that process, we have isolated eleven temperature-sensitive
mutants named ptr1~11 (poly(A)+ RNA transport), which
are defective in nucleocytoplasmic transport of mRNA at the restrictive
@Of those, ptr7 shows pleiotropic phenotypes in addition to the defect in mRNA export, including the defect in the correct 3' end cleavage of the transcripts, fragmentation of the nucleolus and morphological change at the restrictive temperature. Nuclear import of an NLS-GFP protein is also impaired in ptr7, suggesting that the gene product is required for bidirectional transport of macromolecules between the nucleus and the cytoplasm. The ptr7+ gene encodes a 50-kDa protein with an ATP/GTP binding motif. The in vitro binding experiment demonstrated that Ptr7p binds ATP, ADP and GTP.
@To examine the detailed function of Ptr7p, we screened for proteins interacting with Ptr7p by using the yeast two-hybrid assay. As a result, we identified several proteins including ribosomal proteins L21 and S24 as candidates for interacting proteins. Analysis using tagged proteins revealed that Ptr7p binds ribosomal proteins and functional Ptr7p is required for localization of ribosomal proteins in the nucleolus.