Crucial contribution of the multiple copies of the initiator tRNA genes in the fidelity of tRNA fMet selection on the ribosomal P-site in Escherichia coli

Abstract

The accuracy of the initiator tRNA (tRNAfMet) selection in the ribosomal P-site is central to the fidelity of protein synthesis. A highly conserved occurrence of three consecutive G–C base pairs in the anticodon stem of tRNAfMet contributes to its preferential selection in the P-site. In a genetic screen, using a plasmid borne copy of an inactive tRNAfMet mutant wherein the three G–C base pairs were changed, we isolated Escherichia coli strains that allow efficient initiation with the tRNAfMet mutant. Here, extensive characterization of two such strains revealed novel mutations in the metZWV promoter severely compromising tRNAfMet levels. Low cellular abundance of the chromosomally encoded tRNAfMet allows efficient initiation with the tRNAfMet mutant and an elongator tRNAGln, revealing that a high abundance of the cellular tRNAfMet is crucial for the fidelity of initiator tRNA selection on the ribosomal P-site in E. coli. We discuss possible implications of the changes in the cellular tRNAfMet abundance in proteome remodeling.