; The enzyme, Qβ replicase, responsible for the replication of the RNA of;;
Escherichia coli; pahge Qβ, is composed of four nonidentical subunits, three of which, I, III, and IV, are coded for by the bacterial genome, while subunit II is phage-specific.;
Subunit IV is shown to be identical to the protein synthesis elongation factor EF Ts by the following criteria: coelectrophoresis on polyacrylamide gels in sodium dodecyl sulfate and in urea buffers, identity of the first seven amino acids at the amino-terminus, precipitation of sub-unit IV by anti-EF T-factor serum, and stimulation of EF Tu-GDP exchange by subunit IV. Subunit III is shown to be identical to the protein synthesis elongation factor EF Tu by the following criteria: coelectrophoresis on sodium dodecyl sulfate gels, precipitation of EF Tu by anti-Qβ replicase serum, binding of guanine nucleotides, and binding of phenylalanyl-tRNA. In addition, Qβ replicase activity can be reconstituted from subunits I and II with EF Tu and EF Ts.