Mutations in genes downstream of the rpoN gene (encoding σ54) of Klebsiella pneumoniae affect expression from σ54‐dependent promoters

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Abstract
Two open reading frames (ORFs), designated ORF95 and ORF162, downstream of the Klebsiella pneumoniae .sigma.54 structural gene (rponN) have been sequenced and shown to encode polypeptides of 12 kD and 16 kD, respectively. ORFs homologous to ORF95 are present downstream of four out of five rponN genes sequenced to date from a range of Gram-negative bacteria, and ORF162 is also conserved, at least in Pseudomonas putida. Chromosomal mutations have been created in each gene using a kan cassette and both have the same phenotype, i.e. they cause an increase in the level of expression from .sigma.54-dependent promoters. We propose that the products of both genes function to modulate the activity of E.sigma.54, although a physiological role for these proteins has not yet been identified.