Abstract
Sigma S (σ
s
) encoded by
rpoS
is a stationary phase-specific σ subunit of the
Escherichia coli
RNA polymerase holoenzyme. In many
E. coli
strains,
rpoS
has an amber stop as codon 33 (
rpoSAm
), resulting in a 32-amino-acid-long peptide. Nevertheless, suppressor-free
rpoSAm
strains have functional σ
S
. This led us to hypothesize the presence of an intracistronic secondary translational initiation region (STIR) in the
E. coli rpoS
gene. Here, we demonstrate that the STIR is functional and is controlled by the upstream amber stop codon 33. Removal of the primary translational initiation region did not abolish translation from STIR, ruling out translational coupling. Importantly, the functional STIR conferred survival advantage. Taken together, our results reveal a hitherto unknown physiologically significant post-transcriptional process in
E. coli rpoSAm
strains.
