Export and transport of tRNA are coupled to a multi-protein complex

Vigilin is a ubiquitous multi heterogeneous nuclear ribonucleoprotein (hnRNP) K homologous (KH)-domain protein. Here we demonstrate that purified recombinant human vigilin binds tRNA molecules with high affinity, although with limited specificity. Nuclear microinjection experiments revealed for the first time that the immuno-affinity-purified nuclear vigilin core complex (VCCN) as well as recombinant vigilin accelerate tRNA export from the nucleus in human cells. The nuclear tRNA receptor exportin-t is part of the VCCN. Elongation factor (EF)Icc. is enriched in VCCN and its cytoplasmic counterpart VCCC, whereas EF-1 beta, EF-1 gamma and EF-1 delta are basically confined to the VCCC. Our results suggest further that vigilin and exportin-t might interact during tRNA export, provide evidence that the channeled tRNA cycle is already initiated in the nucleus, and illustrate that intracellular tRNA trafficking is associated with discrete changes in the composition of cellular cytoplasmic multiprotein complexes containing tRNA.