Cloning and characterization of the pH 2.5 acid phosphatase gene, appA: cyclic AMP mediated negative regulation

Controlled induction of the RpoS regulon in Escherichia coli, using an RpoS-expressing plasmid

RpoS, an alternative sigma factor produced by many gram-negative bacteria, primarily controls genes that are expressed in stationary phase in response to nutrient deprivation. To test the idea that induction of RpoS in the exponential phase, when RpoS is not normally expressed, increases RpoS-dependent gene expression, we constructed a plasmid carrying the rpoS gene under the control of an IPTG (isopropyl-beta-D-thiogalactopyranoside)-inducible T7lac promoter. Northern and Western analyses revealed that levels of RpoS mRNA and protein, respectively, increased in response to the inducer IPTG. Assays of changes in RpoS-dependent functions (catalase activity and glycogen accumulation), confirmed that induced RpoS was functional in exponential phase and was sufficient for the expression of RpoS-dependent functions. Controlled expression of RpoS and RpoS-dependent genes by plasmid-encoded rpoS may thus offer a useful tool for the study of RpoS-dependent gene expression.

Nucleotide sequence of Escherichia coli katE, which encodes catalase HPII

A 3,466-bp nucleotide sequence containing the katE gene of Escherichia coli has been determined. An open reading frame of 2,259 bp was found and was preceded by a potential ribosome-binding site. The predicted N-terminal sequence agreed with the sequence determined by direct amino acid sequencing, and the predicted direction of transcription was confirmed by expression of the gene cloned in both directions behind a T7 promoter. The start site of transcription was determined to be 127 bp upstream from the start of the open reading frame, and a potential RNA polymerase-binding site similar to a sequence preceding the xthA gene, which is also controlled by the KatF protein, was identified. The predicted sequence of the 753-amino-acid protein was compared with known sequences of other catalases, revealing significant similarity to the shorter catalases, including the residues in the putative active site and residues involved in heme binding.