AUC is used as a start codon in Escherichia coli.

Overexpression of the polymerase II transcription factor E subunit alpha mRNA (TFIIE alpha) in Escherichia coli with the pET3a expression vector [Studier et al., Methods Enzymol. 185 (1990) 60-89] results in the production of a 50-kDa N-truncated polypeptide in addition to the 57-kDa wild-type polypeptide. Microsequencing analysis of the 50-kDa truncated protein and verification of the TFIIE alpha mRNA, showed that a Shine-Dalgarno-like sequence present 200 nucleotides downstream from the normal start codon could direct the use of an internal AUC codon. This codon should thus be added to the list of the non-AUG start codons.