9 Protein Factors Required for the Replication of Phage Qβ RNA In Vitro

Abstract

INTRODUCTION
Despite the apparent simplicity of the RNA bacteriophage, several proteins, both phage and bacterial, are required for the synthesis of Qβ RNA in vitro. As described elsewhere in this volume (see Chapter 7), the polymerase complex alone contains one phage-coded and three host proteins. The specific role of these proteins in Qβ RNA replication is as yet unknown, but as they are always found with active enzyme, it has been suggested that each contributes to polymerase activity. In addition to the polymerase proteins, two additional bacterial proteins not associated with the polymerase and found in uninfected as well as phage-infected E. coli are required in the reaction (Franze de Fernandez, Eoyang and August 1968; Shapiro, France de Fernandez and August 1968). Their function was related solely to the template activity of Qβ RNA as they were not needed for synthesis directed by the Qβ complementary RNA or other templates for the enzyme. The separation of factor fractions from the Qβ polymerase was also described by others (Eikhom and Spiegelman 1967; Eikhom, Stockley and Spiegelman 1968). Moreover, Fedoroff and Zinder (1973) have reported that the f2 poly(G) polymerase required the presence of an additional factor component for polymerase activity with both f2 plus and minus strand templates. This requirement for the f2 enzyme appears to involve proteins different from factor I and II, as the factors were not active in the f2 polymerase system.

We describe below our current knowledge of the factor proteins and more recent data concerning their...