Stem-Loop Structure Synergy in Binding Cellular Proteins to the 5′| Noncoding Region of Poliovirus RNA

Picornavirus RNAs interact with host cellular proteins to direct viral translation initiation by internal ribosome entry. In this study, we analyzed the RNA-protein interactions involving computer-predicted stem-loops F and G (also referred to as V and VI, respectively) of the 5′ NCR of poliovirus RNA. This region of the 5′ NCR harbors part of the putative internal ribosome entry site. We show that a ribonucleoprotein complex involving stem-loop G RNA is composed, at least in part, of a 39-kDa HeLa cell polypeptide which contacts the viral RNA directly. Interestingly, the binding site of a neuronal cell 60-kDa protein, not present in HeLa cells, was mapped specifically to stem-loop G. We also determined that a subset of cellular factors requires a higher order structure synergy before binding to poliovirus RNAs. This was demonstrated by using a longer RNA encompassing both stem-loops F and G in the binding assays. Indeed, a protein with an approximate molecular weight of 36 kDa was shown to interact specifically with these poliovirus sequences. In addition, the role of a cellular polypeptide (p57 or PTB) in poliovirus replication functions was studied. Our results suggest that p57 interactions with stem-loops F-G are not required for internal ribosome binding on poliovirus RNAs.