ASSOCIATION OF EF-Tu.Ts WITH THE OTHER ENZYME SUBUNITS*

Qp replicase is a complex of four nonidentical subunits readily dissociable into two subcomplexes: 30 S ribosomal protein Sl and the phage-coded polypeptide (Subunits I + II) and protein synthesis elongation factors EF-Tu and EF-Ts (Subunits III + IV). The affinity of the two subcomplexes for one another increases with increasing ionic strength. The enzyme is capable of initiation of RNA synthesis with synthetic templates only when in the low ionic strength conformation. Elongation of initiated polynucleotide chains is not affected by ionic strength. Addition of QP RNA to the enzyme also alters its quaternary structure: the EF-Tu.Ts cannot be covalently attached to the other enzyme subunits with bifunctional cross-linking reagents in the presence of RNA. This conformational change is not influenced by ionic strength. The addition of Qfl RNA to the enzyme, does not result in the release of EF-Tu.Ts from the other enzyme subunits: whereas free EF-Tu.Ts binds GDP independently of salt concentration, this binding by Q/3 replicase is sensitive to high ionic strength and remains so in the presence of Qp RNA. Furthermore, RNA does not allow the release of EF-Ts from EF-Tu by GTP as measured by sensitivity of EF-Ts activity to N-ethylmaleimide.