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F plasmid CcdB killer protein ccdB gene mutants coding for non‐cytotoxic proteins which retain their regulatory functions
Author(s) -
Bahassi EI Mustapha,
Salmon Michel A.,
Melderen Laurence,
Bernard Philippe,
Couturier Martine
Publication year - 1995
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1995.tb02278.x
Subject(s) - biology , plasmid , gene , mutant , repressor , genetics , transcription factor
Summary 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 auto‐regulatory 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.