The effect of tRNA derivatives bound with natural or synthetic mRNA on the interaction of Escherichia coli ribosomes with colicin E3.

Ribosomal binding complexes directed by poly(U) or T4 mRNA were formed with aminoacyl-tRNA or its derivatives bound to predominantly the P or A binding site. The defined binding complexes were reacted with colicin E3 and the reaction was assessed by the ability of the complexes to proceed with polypeptide synthesis. The results indicated that only one of the four complexes tested was completely resistant to colicin E3-induced inactivation: that of Phe-tRNA bound in the presence of poly(U) to the A-site. The poly(U) directed complex of AcPhe-tRNA and the T4-mRNA-directed complex at the A-site appeared slightly resistant, while the T4 mRNA initiation complex was inactivated by colicin E3 in a manner similar to non-complexed ribosomes. Colicin E3 added to ribosomes after protein synthesis had been initiated affected the subsequent polymerization in a manner corresponding to the response of the binding complexes. Thus, poly(U)-translating ribosomes were less affected than ribosomes translating the viral mRNA. The vulnerability of natural-mRNA-directed binding complexes to inactivation by colicin E3 is in accord with the mode of inactivation by the colicin in vivo.