UC San Diego

The fucose (fuc) regulon in Escherichia coli encodes proteins necessary for the uptake and metabolism of L-fucose. The regulon is composed of two divergent operons, fucPIK and fucAO, both of which are regulated by the cyclic AMP receptor protein (Crp) and the FucR protein. Under anaerobic conditions, the fucO gene produces an oxidoreductase (OR) that catalyzes the reduction of L-lactaldehyde (LA; a metabolic intermediate) and disseminates propanediol (PPD) as a byproduct. Additionally, OR can oxidize PPD to LA. However, E. coli cannot utilize PPD as a carbon source because FucR is absent. IS5 insertion between the fucPIK and fucAO operons causes the constitutive activation of fucAO while fucPIK becomes non-inducible, allowing E. coli to utilize PPD as a sole carbon source. The mechanism behind the activation of fucAO by IS5 remains unclear. In this study, we demonstrate the formation of a functional hybrid promoter following IS5 insertion, which drives the downstream fucAO operon. Our findings indicate that the promoter is generated using a DNA sequence directly upstream of the IS5 element as the '-35' region and a DNA sequence within the transposase promoter as the '-10' region, with the transcriptional start site (TSS) of the hybrid promoter being identical to the TSS of the transposase promoter. Additionally, we examined how the fuc regulon is regulated by analyzing the wild-type fucAO promoter. This involved identifying the CRP binding site that regulates the fucAO promoter, the genuine TSS of the fucAO promoter, and the possible binding site for FucR.