NUCLEAR MESSENGER-RNA EXPORT REQUIRES COMPLEX-FORMATION BETWEEN MEX67P AND MTR2P AT THE NUCLEAR-PORES

We have identified between Mex67p and Mtr2p a complex which is essenti al for mRNA export. This complex, either isolated from yeast or assemb led in Escherichia coli, can bind in vitro to RNA through Mex67p. In v ivo, Mex67p requires Mtr2p for association with the nuclear pores, whi ch can be abolished by mutating either MEX67 or MTR2. In all cases, de tachment of Mex67p from the pores into the cytoplasm correlates with a strong inhibition of mRNA export. At the nuclear pores, Nup85p repres ents one of the targets with which the Mex67p-Mtr2p complex interacts. Thus, Mex67p and Mtr2p constitute a novel mRNA export complex which c an bind to RNA via Mex67p and which interacts with nuclear pores via M tr2p.