In vitro copying of viral positive strand RNA by poliovirus replicase. Characterization of the reaction and its products.

Poliovirus replicase can be isolated in a form which depends on either oligo(U) or on a host cell protein for the initiation of copying of poliovirion (plus strand) RNA. The product of replicase reactions--initiated either with host factor or with oligo(U)--includes full length (35 S) RNA molecules, largely in double-stranded form, which contain the ribonuclease T1-resistant oligonucleotides of the poliovirus minus strand. For the oligo(U)-stimulated reaction, it is shown that the oligo(U) primer is covalently associated with full length product at its 5'-end. For either the host factor- or oligo(U)-dependent reactions, full length molecules appear only after 15 min of synthesis. The fraction of 35 S product is increased by raising the concentration of the limiting nucleoside triphosphate. The reaction is inhibited by as little as 100 mM salt, although it is stimulated by low (20 mM) salt concentrations. Zinc stimulates overall synthesis, but not the rate of appearance of full length molecules; the reaction is inhibited by agents which chelate zinc. Although synthesis of full length products occurs much more slowly than in the infected cell, this soluble system appears to mimic quite faithfully the initial steps of poliovirus replication.