Rare initiation codons are regulators of expression of the rpoC gene

Translation of the rpoC genes in Escherichia coli and Salmonella typhimurium is known to start from the GUG codon. Now, using toeprint analysis we have shown UUG to be the initiation codon of the Pseudomonas putida rpoC gene. IF3 does not seem to proofread initiation at the UUG codon. The rpoC genes of P. putida, E. coli, and S. typhimurium, which use rare start codons, have strong SD-domains AGGAGG (P. p.) and GGGAG (E. c., S. t.), optimal seven-nucleotide spacing between SD and start codons, and good second codon AAA. We suggest that rpoC presents an infrequent case of the regulation of translation initiation by selecting the start codon.