title: F plasmid CcdB killer protein: ccdB gene mutants coding for non-cytotoxic proteins which retain their regulatory functions.
abstract: The ccd locus of the F plasmid codes for two gene products, CcdA and CcdB, which contribute to the plasmid's high stability by post-segregational killing of plasmid-free bacteria. Like the quinolones, the CcdB protein is a poison of the DNA-topoisomerase II complexes, while CcdA acts as an antidote against CcdB. In addition to these poison-antipoison properties, the CcdA and CcdB proteins act together at transcription level to repress their own synthesis. In this work, we have isolated, in vivo, and characterized several non-killer CcdB mutants. All missense mutations which inactivate CcdB killer activity are located in the region coding for the last three C-terminal residues. However, the resulting mutant CcdB proteins retain their autoregulatory properties. We conclude that the last three C-terminal residues of CcdB play a key role in poisoning but are not involved in repressor formation.
authors.affiliation: Département de Biologie Moléculaire, Université Libre de Bruxelles, Rhode-Saint-Genèse, Belgium.
authors.forename: E M
authors.initials: EM
authors.lastname: Bahassi
authors.forename: M A
authors.initials: MA
authors.lastname: Salmon
authors.forename: L
authors.initials: L
authors.lastname: Van Melderen
authors.forename: P
authors.initials: P
authors.lastname: Bernard
authors.forename: M
authors.initials: M
authors.lastname: Couturier
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D001427:Bacterial Toxins / Q000096:biosynthesis / Q000235:genetics*; D001483:Base Sequence; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D005144:F Factor / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation / Q000502:physiology*; D009875:Operator Regions, Genetic / Q000235:genetics; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics; D013489:Suppression, Genetic / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; C068355:CcdA protein, Bacteria; C068356:CcdB protein, Plasmid F; D004269:DNA, Bacterial; D012097:Repressor Proteins