The effect of tryptrophan on nucleocytoplasmic translocation of RNA in rat liver.

The effect of the administration of tryptophan on the transport of nuclear poly (A)-containing mRNA to the cytoplasm in rat liver was investigated. Administration of tryptophan to fasted rats pretreated with cordycepin and actinomycin D led to decreased levels of nuclear poly (A)-mRNA and a concomitant increase in the levels of polyribosomal poly (A)-mRNA in the cytoplasm as determined by measuring in vivo incorporation of labeled precursors into hepatic RNA. Using isolated hepatic nuclei of rats prelabeled in vivo with [14C]orotic acid, there was greater release of labeled poly(A)-mRNA into the incubation medium from nuclei of tryptophan-treated rats than from nuclei of control animals. The increased release of RNA from hepatic nuclei of tryptophan-treated animals was not related to the cell sap present in the media since cell saps from livers of control and experimental rats gave similar results. These results support earlier findings which suggest that in the rat tryptophan increases the rate of translocation of hepatic poly(A)-mRNA from nucleus to cytoplasm.