Interaction of host-coded and virus-coded polypeptides in RNA phage replication
Journal Article
Overview
abstract
; The enzymes responsible for replication of the RNA of the single-stranded RNA bacteriophages contain, in addition to one phage-coded polypeptide, three host-coded polypeptides taken from the protein biosynthetic machinery: ribosomal protein S1 and the elongation factors Tu and Ts. While S1 performs a function in RNA replication derived from its protein synthetic function, mRNA binding, the reactions catalysed by the elongation factors in protein synthesis are apparently dispensible for RNA replication. In the replicase, these polypeptides, acting as the EF-Tu∙Ts complex, play a fundamental structural role. Replacement of the endogenous EF-Tu with mutant EF-Tu, itself stable, causes the RNA replicase to become unstable. The possibility that EF-Tu∙Ts is solely a structural protein in the RNA replicase is suggested by experiments showing that a variety of modifications of the elongation factors can be tolerated without loss of RNA synthetic capacity. In fact, EF-Tu∙Ts from distantly related bacterial species can substitute for; E; .; coli; EF-Tu∙Ts in RNA replicase. Evidence is presented that the high; in vitro; template specificity of Qβ replicase may be accomplished through modulation of the level of GTP required for initiation of transcription. Different natural and synthetic RNAs require quite different GTP concentrations. Mn; 2+; ions, which extend the range of templates transcribed by Qβ replicase, lower the requirement for GTP. High ionic strength, which alters the conformation of Qβ replicase such that template specificity is increased, raises the GTP requirement. An additional host coded protein required for; in vitro; Qβ RNA replication, host factor (HF), interacts specifically with Qβ RNA. This polypeptide acts by allowing Qβ replicase to initiate RNA synthesis with Qβ RNA at reduced GTP concentration.;
