KorB switching from DNA-sliding clamp to repressor mediates long-range gene silencing in a multi-drug resistance plasmid
Thomas C. McLean, Francisco de Asís Balaguer, Joshua Chandanani, Christopher M. Thomas, Clara Aicart-Ramos, Sophia Burick, Paul Dominic B. Olinares, Giulia Gobbato, Julia E. A. Mundy, Brian T. Chait, David M. Lawson, Seth A. Darst, Elizabeth A. Campbell, Fernando Moreno‐Herrero, Tung B. K. Le
Abstract
Examples of long-range gene regulation in bacteria are rare and generally thought to involve DNA looping. Here, using a combination of biophysical approaches including X-ray crystallography and single-molecule analysis for the KorB-KorA system in Escherichia coli, we show that long-range gene silencing on the plasmid RK2, a source of multi-drug resistance across diverse Gram-negative bacteria, is achieved cooperatively by a DNA-sliding clamp, KorB, and a clamp-locking protein, KorA. We show that KorB is a CTPase clamp that can entrap and slide along DNA to reach distal target promoters up to 1.5 kb away. We resolved the tripartite crystal structure of a KorB-KorA-DNA co-complex, revealing that KorA latches KorB into a closed clamp state. DNA-bound KorA thus stimulates repression by stalling KorB sliding at target promoters to occlude RNA polymerase holoenzymes. Together, our findings explain the mechanistic basis for KorB role switching from a DNA-sliding clamp to a co-repressor and provide an alternative mechanism for long-range regulation of gene expression in bacteria.