POLY (RC) BINDING-PROTEIN-2 FORMS A TERNARY COMPLEX WITH THE 5'-TERMINAL SEQUENCES OF POLIOVIRUS RNA AND THE VIRAL 3CD PROTEINASE

Poly(rC) binding protein 2 (PCBP2) forms a specific ribonucleoprotein (RNP) complex with the 5'-terminal sequences of poliovirus genomic RNA , as determined by electrophoretic mobility shift assay. Mutational an alysis showed that binding requires the wild-type nucleotide sequence at positions 20-25. This sequence is predicted to localize to a specif ic stem-loop within a cloverleaf-like secondary structure element at t he 5'-terminus of the viral RNA. Addition of purified poliovirus 3CD t o the PCBP2/RNA binding reaction results In the formation of a ternary complex, whose electrophoretic mobility is further retarded. These pr operties are consistent with those described for the unidentified cell ular protein in the RNP complex described by Andino et al. (Andino R, Rieckhof GE, Achacoso FL, Baltimore D, 1993, EMBO J 12:3587-3598). Dic istronic RNAs containing mutations in the 5' cloverleaf-like structure of poliovirus that abate PCBP2 binding show a decrease in RNA replica tion and translation of gene products directed by the poliovirus 5' no ncoding region in vitro, suggesting that the interaction of PCBP2 with these sequences performs a dual role in the virus life cycle by facil itating both viral protein synthesis and initiation of viral RNA synth esis.