Abstract
Highly purified coliphage Qbeta replicase when incubated without added template synthesizes self-replicating RNA species in an autocatalytic reaction. In this paper we offer strong evidence that this RNA production is directed by templates generated de novo during the lag phase. Contamination of the enzyme by traces of RNA templates was ruled out by the following experimental results: (1) Additional purification steps do not eliminate this RNA production. (2) The lag phase is lengthened to several hours by lowering substrate or enzyme concentration. At a nucleoside triphosphate concentration of 0.15 mM no RNA is produced although the template-directed RNA synthesis works normally. (3) Different enzyme concentrations lead to RNA species of completely different primary structure. (4) Addition of oligonucleotides or preincubation with only three nucleoside triphosphates affects the final RNA sequence. (5) Manipulation of conditions during the lag phase results in the production of RNA structures that are adapted to the particular incubation conditions applied (e.g., RNA resistant to nuclease attack or resistant to inhibitors or even RNAs "addicted to the drug," in the sense that they only replicate in the presence of a drug like acridine orange). RNA species obtained in different experiments under optimal incubation conditions show very similar fingerprint patterns, suggesting the operation of an instruction mechanism. A possible mechanism is discussed.