The transactivation region of the Fis protein that controls site-specific DNA inversion contains extended mobile beta -hairpin arms

Abstract

The Fis protein regulates site‐specific DNA inversion catalyzed by a family of DNA invertases when bound to a cis‐acting recombinational enhancer. As is often found for transactivation domains, previous crystal structures have failed to resolve the conformation of the N‐terminal inversion activation region within the Fis dimer. A new crystal form of a mutant Fis protein now reveals that the activation region contains two β‐hairpin arms that protrude over 20 Å from the protein core. Saturation mutagenesis identified the regulatory and structurally important amino acids. The most critical activating residues are located near the tips of the β‐arms. Disulfide cross‐linking between the β‐arms demonstrated that they are highly flexible in solution and that efficient inversion activation can occur when the β‐arms are covalently linked together. The emerging picture for this regulatory motif is that contacts with the recombinase at the tip of the mobile β‐arms activate the DNA invertase in the context of an invertasome complex.