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Speaker Dr Tung Le, Group Leader, Department of Molecular Micorbiology, John Innes Centre, Norwich

Title How to manage the complicated life of a multi-drug-resistance plasmid?

Host Julien Bergeron

Abstract RK2, and its related plasmids, confer multi-drug resistance to a wide range of clinically significant Gram-negative bacteria including Pseudomonas aeruginosa, one of the six ESKAPE pathogens. KorB is an essential transcriptional repressor of the RK2 plasmid. Canonically, repressors bind at, or extremely close to, the RNA polymerase (RNAP) binding site and prevent transcription through steric hindrance or RNAP interference. However, KorB can bind over a kilobase away from the RNAP binding site and still exert transcriptional repression. We have demonstrated that KorB binds the nucleotide CTP and undergoes a conformation change which results in a sliding clamp mechanism. This sliding allows KorB to traverse huge distances along the plasmid DNA to interact with RNAP. Intriguingly KorB also cooperates with small accessory proteins which can entrap KorB at the RNAP binding site, halting sliding and synergistically increasing transcriptional repression. This sliding and trapping mechanism appears to be conserved across all domains of life. For example, the bacteriophage T4 late promoter complex employs a sliding activator whilst recent work on the eukaryotic chromosome-associated complex cohesin has revealed that CTCF acts as a clamp to unilaterally prevent loop extrusion and conserves distal gene regulation.

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