Role of 16S ribosomal RNA methylations in translation initiation in Escherichia coli

Abstract

Translation initiation from the ribosomal P‐site is the specialty of the initiator tRNAs (tRNA^fMet). Presence of the three consecutive G‐C base pairs (G29‐C41, G30‐C40 and G31‐C39) in their anticodon stems, a highly conserved feature of the initiator tRNAs across the three kingdoms of life, has been implicated in their preferential binding to the P‐site. How this feature is exploited by ribosomes has remained unclear. Using a genetic screen, we have isolated an Escherichia coli strain, carrying a G122D mutation in folD, which allows initiation with the tRNA^fMet containing mutations in one, two or all the three G‐C base pairs. The strain shows a severe deficiency of methionine and S‐adenosylmethionine, and lacks nucleoside methylations in rRNA. Targeted mutations in the methyltransferase genes have revealed a connection between the rRNA modifications and the fundamental process of the initiator tRNA selection by the ribosome.