Poliovirus RNA-Dependent RNA Polymerase Synthesizes Full-Length Copies of Poliovirion RNA, Cellular mRNA, and Several Plant Virus RNAs In Vitro

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Abstract
The poliovirus RNA-dependent RNA polymerase was active on synthetic homopolymeric RNA templates and on every natural RNA tested. The polymerase copied poly(A).cntdot.oligo(U), poly(C).cntdot.oligo(I), and poly(I).cntdot.oligo(C) templates to about the same extent. The observed activity on poly(U).cntdot.oligo(A) was .apprx. 4-fold less. Full-length copies of both poliovirion RNA and a wide variety of other polyadenylated RNA were synthesized by the polymerase in the presence of oligo(U). Polymerase elongation rates on poliovirion RNA and a heterologous RNA (squash mosaic virus RNA) were about the same. Changes in the Mg2+ concentration affected the elongation rates on both RNA to the same extent. With 2 non-polyadenylated RNA (tobacco mosaic virus RNA and brome mosaic virus RNA3), the results were different. The purified polymerase synthesized a subgenomic-sized product RNA on brome mosaic virus RNA3 in the presence of oligo(U). This product RNA appeared to initiate on oligo(U) hybridized to an internal oligo(A) sequence in brome mosaic virus RNA3. No oligo(U)-primed product was synthesized on tobacco mosaic virus RNA. When partially purified polymerase was used in place of the completely purified enzyme, some olgio(U)-independent activity was observed on the brome mosaic virus and tobacco mosaic virus RNA. The size of the product RNA from these reactions suggested that at least some of the product RNA was full-sized and covalently linked to the template RNA. Thus, the polymerase was found to copy many different types of RNA and to make full-length copies of the RNA tested.