Mtr2 is a monomeric, dual-action, RNA-shuttle protein found in yeasts. Transport across the nuclear-cytoplasmic membrane is via the macro-molecular membrane-spanning nuclear pore complex, NPC. The pore is lined by a subset of NPC members called nucleoporins that present FG (Phe-Gly) receptors, characteristically GLFG and FXFG motifs, for shuttling RNAs and proteins. RNA cargo is bound to soluble transport proteins (nuclear export factors) such as Mex67 in yeasts, and TAP in metazoa, which pass along the pore by binding to successive FG receptors. Mtr2 when bound to Mex67 maximises this FG-binding. Mtr2 also acts independently of Mex67 in transporting the large ribosomal RNA subunit through the pore [1].

1: The Mtr2-Mex67 NTF2-like domain complex. Structural insights into a dual role of Mtr2 for yeast nuclear export. Senay C, Ferrari P, Rocher C, Rieger KJ, Winter J, Platel D, Bourne Y; J Biol Chem. 2003;278:48395-48403. PMID:14504280