COMPLEMENTATION OF DEFECTIVE PICORNAVIRUS INTERNAL RIBOSOME ENTRY SITE (IRES) ELEMENTS BY THE COEXPRESSION OF FRAGMENTS OF THE IRES

Mutant forms of the encephalomyocarditis virus (EMCV) internal ribosom e entry site (IRES) have been produced and shown to be severely defect ive in directing internal initiation of protein synthesis within cells using the vaccinia/T7 RNA polymerase system. Mutants in different reg ions of the IRES were complemented in trans by coexpression of the int act EMCV IRES but not by coexpression of the related IRES elements fro m Theiler's murine encephalomyelitis virus (another cardiovirus) or fr om foot-and-mouth disease virus. Distinct, truncated regions of the EM CV IRES, insufficient to direct internal initiation, were also shown t o complement defective EMCV IRES elements. it was necessary for the co mplementing molecule, whether truncated or full length, to be expresse d in the positive sense orientation. RT-PCR analysis provided no suppo rt for the idea that any recombination event was responsible for the c omplementation. The data suggest that multiple activities are performe d by distinct functional entities within the IRES in the process of in ternal initiation of protein synthesis. At least some of these differe nt functions may be achieved by different molecules acting in trans. ( C) 1997 Academic Press