Mex67p of Schizosaccharomyces pombe interacts with Rae1p in mediating mRNAexport

We identified the Schizosaccharomyces pombe mex67 gene (spmex67) as a multi copy suppressor of rae1-167 nup184-1 synthetic lethality and the rae1-167 t s mutation, spMex67p, a 596-amino acid-long protein, has considerable seque nce similarity to the Saccharomyces cerevisiae Mex67p (scMex67p) and human Tap. In contrast to seMEX67, spmex67 is essential for neither growth nor nu clear export of mRNA. However, an spmex67 null mutation (Delta mex67) is sy nthetically lethal with the rae1-167 mutation and accumulates poly(A)(+) RN A in the nucleus. We identified a central region (149 to 505 amino acids) w ithin spMex67p that associates with a complex containing Rae1p that complem ents growth and mRNA export defects of the rae1-167 Delta mex67 synthetic l ethality. This region is devoid of RNA-binding, N-terminal nuclear localiza tion, and the C-terminal nuclear pore complex-targeting regions. The (149-5 05)-green fluorescent protein (GFP) fusion is found diffused throughout the cell. Overexpression of spMex67p inhibits growth and mRNA export and resul ts in the redistribution of the diffused localization of the (149-505)-GFP fusion to the nucleus and the nuclear periphery. These results suggest that spMex67p competes for essential mRNA export factor(s). Finally we propose that the 149-505 region of spMex67p could act as an accessory factor in Rae 1p-dependent transport and that spMex67p participates at various common ste ps with Rae1p export complexes in promoting the export of mRNA.