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.