Efflux of RNA from Resealed Nuclear Envelope Ghosts

mRNA translocation across the nuclear envelope and the appropriate signal-receptor interactions have been studied using resealed rat liver nuclear envelope ghosts (RNEG). We compared export kinetics of nonadenylated (tRNAs, histone-2 poly(A) − mRNA), and adenylated RNAs (poly(A) + tRNAs, synthetic histone-2 poly(A)+mRNA, albumin mRNA, β-globin poly(A) +mRNA and a total poly(A) + mRNA extract from rat liver cells). ATP-dependent export of mRNAs and of total poly(A) (+) RNA was prevented by inhibitors of a nuclear envelope NTPase. All adenylated RNA species competed with each other for export, but nonadenylated RNAs did not. This indicates the existence of different translocation mechanisms for different RNA species with their appropriate nuclear envelope associated RNA receptors involved in export. The attachment of a poly(A) 250 sequence at the 3′-end of tRNA or histone messenger masks the intrinsic RNA export signal of nonadenylated RNAs and results in efflux comparable to that of β-globin poly(A) + mRNA. The attachment on oligo(A) 5 does not have any comparable effect of nonadenylated RNA translocation. Export of all polyadenylated RNAs from RNEGs is blocked by a monoclonal antibody, which is directed against an intranuclear envelope poly(A) binding protein. The results suggest that the pore complexes do not select RNAs for export to the cytoplasm and are therefore not responsible for nuclear restriction of mRNA precursors.