A comparison of eukaryotic viral 5′-leader sequences as enhancers of mRNA expressionin vivo

Abstract

The 5′-untranslated leader, sequences of several plant RNA viruses, and a portion of the 5′-leader of an animal retrovirus, were tested for their ability to enhance expression of contiguous open reading frames for chloramphenicol acetyltransferase (CAT) or β-glucuronidase (GUS) in tobacco mesophyll protoplasts, Escherichia coli and oocytes of Xenopus laevis. Translation of capped or uncapped transcripts was substantially enhanced in almost all systems by the leader sequence of either the U1 or SPS strain of TMV. All leader sequences, except that of TYMV, stimulated expression of 5′-capped GUS mRNA with the native prokaryotic initiation codon context, in electroporated protoplasts. Only the TMV leaders enhanced translation of uncapped GUS mRNAs in protoplasts and increased expression of uncapped CAT mRNA in microinjected X. laevis oocytes. In oocytes, the TYMV leader sequence was inhibitory.