EFFECTS OF POLIOVIRUS 3AB PROTEIN ON 3D POLYMERASE-CATALYZED REACTION

Poliovirus RNA replication requires the activities of a viral RNA-depe ndent RNA polymerase, 3D(pol), in conjunction with several additional viral and likely cellular proteins. The importance of both the 3A and 3B coding regions has been documented previously by genetic tests, and their biochemical activities have been the subject of several recent investigations. In this study, we examined the previously reported sti mulation of 3D-catalyzed RNA synthesis by 3AB, We show that 3AB does n ot stimulate RNA synthesis on templates that are stably base paired to a primer, indicating that 3AB does not stabilize or otherwise activat e 3D(pol) for chain elongation. Similarly, it does not alter the kinet ic parameters or binding affinities of 3D for substrates. In the absen ce of a primer, or in the presence of a primer that does not form a st able hybrid with the template, 3AB increases the utilization of 3'-hyd roxyl termini as sites for chain elongation by 3D, and thereby stimula tes RNA synthesis, 3AB may interact with and stabilize these sites and /or may recruit 3D(pol) to the site, resulting in stimulation of the i nitiation of elongation events. We propose that this activity is requi red for stabilizing weak interactions that occur during nucleotidyl-pr otein-primed initiation events in the viral RNA replication complex.