title: Effect of supercoiling on the λ switch.
abstract: The lysogenic state of the λ switch is exceptionally stable, still, it is capable of responding to DNA-damage and rapidly enter the lytic state. We invented an assay where PNA mediated tethering of a plasmid allowed for single molecule investigations of the effect of supercoiling on the efficiency of the epigenetic λ switch. Compared with non-supercoiled DNA, the presence of supercoils enhances the CI-mediated DNA looping probability and renders the transition between the looped and unlooped states steeper, thus increasing the Hill coefficient. Interestingly, the transition occurs exactly at the CI concentration corresponding to the minimum number of CI molecules capable of maintaining the pRM-repressed state. Based on these results we propose that supercoiling maintains the pRM-repressible state as CI concentration decline during induction and thus prevent autoregulation ofcIfrom interfering with induction.
authors.affiliation: The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.
authors.forename: Kamilla
authors.initials: K
authors.lastname: Norregaard
authors.affiliation: The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.
authors.forename: Magnus
authors.initials: M
authors.lastname: Andersson
authors.affiliation: The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.
authors.forename: Kim
authors.initials: K
authors.lastname: Sneppen
authors.affiliation: Department of Cellular and Molecular Medicine; Faculty of Health and Sciences; Copenhagen, Denmark.
authors.forename: Peter Eigil
authors.initials: PE
authors.lastname: Nielsen
authors.affiliation: The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.
authors.forename: Stanley
authors.initials: S
authors.lastname: Brown
authors.affiliation: The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.
authors.forename: Lene B
authors.initials: LB
authors.lastname: Oddershede
keywords: CI protein; PNA; cooperativity; epigenetics; supercoiling; tethered particle motion; λ switch