An Intermediate in the Synthesis of Poliovirus RNA

Abstract

The pairwise complementarity of the nucleotide residues in nucleic acids provides a simple mechanism for the specification of the sequence of residues in a nucleic acid. A molecule with a given sequence will specify a molecule with a complementary sequence and, in turn, the complementary molecule can specify the sequence of the original one. In the case of single-stranded RNA viruses, it is thus likely that a strand of complementary RNA will be the intracellular template for the synthesis of viral RNA (the molecule which exists in mature particles). This argument is strengthened by the finding of double-stranded RNA in cells infected with single-stranded RNA viruses. The hypothesis that the complementary molecule of RNA, in a double-stranded RNA, is the template for viral RNA synthesis requires that there be a region of hydrogen bonding between the growing molecule of viral RNA and the complementary RNA. As the new chain of viral RNA elongates, either it displaces the viral strand of the double-stranded RNA or it is not hydrogen-bonded except in proximity to the growing point. In either case, the growing strand of viral RNA plus its template will form a complex which will be partially single- and partially double-stranded. Since more than one molecule of nascent viral RNA could be attached to one double-stranded molecule, such complexes might be fairly large and easily distinguishable from true double-stranded RNA by their content of single-stranded RNA. We shall present evidence in this paper for the existence of such a complex of single- and double-stranded RNA in cells infected with poliovirus. It is similar to a structure first identified in bacteria infected with an RNA bacteriophage which was named the replicative intermediate (RI). We shall retain this nomenclature.