Intermediates in the synthesis of TolC protein include an incomplete peptide stalled at a rare Arg codon.

TolC is a minor outer membrane protein of Escherichia coli K 12 and is initially synthesized as a precursor. A distinct intermediate polypeptide of Mr about 46 000 was consistently observed at the initial stages of biosynthesis. The further elongation of this peptide can be blocked by chloramphenicol. We have investigated the cause of the temporary accumulation of the 46 000-Mr intermediate and we postulate that the presence of a rare codon AGA (Arg) at codon 402 of the tolC mRNA halts translating ribosomes owing to a limiting amount of the tRNAArg (AGA) species in the cell. The translation of tolC mRNA can be increased by providing T4 tRNAArg (AGA), encoded on a plasmid.