Structure and Mode of Action ofkikA,a Genetic Region Lethal toKlebsiella oxytocaand Associated with Conjugative Antibiotic-Resistance Plasmids of the IncN Group

Abstract Transmission of conjugative plasmids of the IncN group into Klebsiella oxytoca, but not into Escherichia coli, results in the marked reduction of viability of the recipients. In the plasmid pCU1 a 500-bp locus called kikA has the major role in determining this phenotype. Expression of two open reading frames ( orf104 and orf70 ) is required for the Kik + phenotype and they can function in cis or in trans. orf104 encodes a 8.9-kDa soluble protein which is translocated into the periplasm. orf70 encodes a 7.6-kDa soluble protein which is found in the cytoplasm. The expression of the kikA region from its natural promoter(s) is positively regulated at the level of transcription by an additional plasmid locus which is located within the tra region. Further experiments show that the action of kikA causes reversible growth inhibition but does not affect cellular respiration and does not induce any morphological changes of the host cell.