Iron mediated methylthiolation of tRNA as a regulator of operon expression inEscherichia coli

Abstract

E. coli growing in the presence of iron-binding proteins produced tRNA^trp and tRNA^phe molecules containing 1⁶A instead of ms²i⁶A adjacent to the anticodon. These undermodified tRNAs functioned less efficiently than the fully modified molecules when translating synthetic polynucleotides containing contiguous codons in an in vitro system, but did not limit the translation of MS2 RNA. We examined the possibility that the altered tRNAs with lowered translational efficiencies could relieve transcription termination at the trp and phe attenuators and lead to increased operon expression under iron restricted conditions. Using trpR mutants we found that there was indeed greater expression of the trp operon during iron restricted growth. This increase was attributable solely to the tRNA alteration induced by iron restriction.