Bahassi E M, Salmon M A, Van Melderen L, Bernard P, Couturier M
Département de Biologie Moléculaire, Université Libre de Bruxelles, Rhode-Saint-Genèse, Belgium.
Mol Microbiol. 1995 Mar;15(6):1031-7. doi: 10.1111/j.1365-2958.1995.tb02278.x.
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.
F质粒的ccd位点编码两种基因产物，CcdA和CcdB，它们通过对无质粒细菌的后分离杀伤作用来提高质粒的稳定性。与喹诺酮类药物一样，CcdB蛋白是DNA拓扑异构酶II复合物的毒药，而CcdA则作为CcdB的解毒剂。除了这些毒-解毒特性外，CcdA和CcdB蛋白在转录水平共同作用以抑制它们自身的合成。在这项工作中，我们在体内分离并鉴定了几个非杀伤性CcdB突变体。所有使CcdB杀伤活性失活的错义突变都位于编码最后三个C末端残基的区域。然而，产生的突变CcdB蛋白保留了它们的自动调节特性。我们得出结论，CcdB的最后三个C末端残基在中毒中起关键作用，但不参与阻遏物的形成。
