INHIBITION OF MESSENGER-RNA EXPORT IN VERTEBRATE CELLS BY NUCLEAR EXPORT SIGNAL CONJUGATES

Leucine-rich nuclear export signals (NESs) are recognized by the NES r eceptor exportin 1 and are central to the export of multiple shuttling proteins and RNAs, The export of messenger RNA in vertebrates was, ho wever, thought to occur by a different pathway, because inhibition by injection of a synthetic Rev NES conjugate could not be demonstrated, Here we find that peptide conjugates composed of the NES of either pro tein kinase A inhibitor protein (PKI) or the HIV-I Rev protein, when c oupled to human serum albumin, are potent inhibitors of mRNA and small nuclear RNA export, These results provide direct evidence that mRNA e xport in vertebrates depends on interactions between an NES and its co gnate NES receptors, PKI NES conjugates are significantly more efficie nt at inhibiting RNA export than are REV NES conjugates, indicating th at different NESs mag have different abilities to promote protein and RNA export, Surprisingly, an expected control conjugate containing the mutant Rev NES sequence M10 strongly inhibited the export of intronle ss dihydrofolate reductase mRNA, Nuclear injection of NES peptide conj ugates led to mislocalization to the nucleus of 10-20% of the cytoplas mic Ran GTPase-binding protein (RanBP1) indicating that RanBP1 shuttle s between the nucleus and the cytoplasm via an NES pathway, These resu lts demonstrate that in vertebrates the export of mRNA, like that of s mall nuclear RNA, 5S rRNA, and transport factors such as RanBP1, emplo ys NES-mediated molecular machinery.