Structural organization of a viral IRES depends on the integrity of the GNRA motif

A UNCG sequence does not functionally substitute the GNRA motif for IRES activity. Bicistronic constructs containing the FMDV IRES bearing the wild-type GUAA sequence or the indicated UNCG substitution between CAT and luciferase were transfected into BHK-21 cells. Relative IRES activity was calculated as the luciferase/CAT activity in each extract, made relative to that observed in the full-length wild-type IRES.