EFFICIENT EXPRESSION OF A PROTEIN-CODING GENE UNDER THE CONTROL OF ANRNA POLYMERASE-I PROMOTER

In mammalian cells, RNA polymerase I transcripts are uncapped and reta in a polyphosphate 5' terminus. It is probably for this reason that th ey are poorly translated as messenger RNA. We show in this report that insertion of an Internal Ribosome Entry Site (IRES) into the 5' leade r of an RNA polymerase I transcript overcomes the block to translation , presumably by substituting for the 5' trimethyl G cap. Addition of a n SV40 polyA addition signal also enhances protein production from the RNA polymerase I transcript. RNA Polymerase I driven expression vecto rs containing both elements produce protein at levels comparable to th at produced from RNA polymerase II driven expression vectors which uti lize a retroviral LTR. RNA Polymerase' I driven expression vectors may have a variety of uses both for basic research and for practical expr ession of recombinant proteins.