Promoters and autogenous control of the Escherichia coli hupA and hupB genes.

Three start sites and a single start site for transcription of the hupB and hupA genes, respectively, have been identified in Escherichia coli. Preceding the RNA start sites are DNA sequences that conform to canonical promoter consensus sequences. The two most upstream promoters of the hupB gene function in vivo at comparable efficiency, while the third is not expressed significantly. Both hupB and hupA genes possess a DNA sequence with a rho-independent transcriptional terminator in their respective regions downstream from the coding regions. The hup genes are both transcribed in vivo into monocistronic mRNA molecules. Upon introduction of an HU-overproducing plasmid carrying either the hupB or the hupA gene into the wild-type and hup single deletion mutants, the intracellular levels of mRNA from the chromosomal hup genes are reduced. The HU-1 and HU-2 proteins both repress both hup genes, repression of the hupB gene being less efficient. The HU protein selectively represses mRNA synthesis starting at the hup promoters in the hupB promoter-CmR and hupA promoter-KmR fusion genes, but does not have a negative regulatory effect on mRNA synthesis from the true CmR and KmR promoters. These findings suggest that the signals for the actions of HU proteins are located in the DNA regions upstream from the sites near the 5' extremities of the coding regions of the hupB and hupA genes.