Replacement of L7/L12.L10 protein complex in Escherichia coli ribosomes with the eukaryotic counterpart changes the specificity of elongation factor binding

The L8 protein complex consisting of L7/L12 and L10 in Escherichia coli rib osomes is assembled on the conserved region of 23 S rRNA termed the GTPase associated domain. We replaced the L8 complex in E, coli 50 S subunits with the rat counterpart P protein complex consisting of P1, P2, and P0. The L8 complex was removed from the ribosome with 50% ethanol, 10 mM MgCI2, 0.5 M NH4Cl, at 30 degrees C, and the rat P complex bound to the core particle. Binding of the P complex to the core was prevented by addition of RNA fragm ent covering the GTPase-associated domain of E, coli 23 S rRNA to which rat P complex bound strongly, suggesting a direct role of the RNA domain in th is incorporation. The resultant hybrid ribosomes showed eukaryotic transloc ase elongation factor (EF)-2-dependent, but not prokaryotic EF-G-dependent, GTPase activity comparable with rat 80 S ribosomes. The EF-2-dependent act ivity was dependent upon the P complex binding and was inhibited by the ant ibiotic thiostrepton, a ligand for a portion of the GTPase-associated domai n of prokaryotic ribosomes, This hybrid system clearly shows significance o f binding of the P complex to the GTPase-associated RNA domain for interact ion of EF-2 with the ribosome. The results also suggest that E, coli 23 S r RNA participates in the eukaryotic translocase-dependent GTPase activity in the hybrid system.