title: Dual architectural roles of HU: formation of flexible hinges and rigid filaments.
abstract: The nucleoid-associated protein HU is one of the most abundant proteins in Escherichia coli and has been suggested to play an important role in bacterial nucleoid organization and regulation. Although the regulatory aspects of HU have been firmly established, much less is understood about the role of HU in shaping the bacterial nucleoid. In both functions (local) modulation of DNA architecture seems an essential feature, but information on the mechanical properties of this type of sequence-independent nucleoprotein complex is scarce. In this study we used magnetic tweezers and atomic force microscopy to quantify HU-induced DNA bending and condensation. Both techniques revealed that HU can have two opposing mechanical effects depending on the protein concentration. At concentrations <100 nM, individual HU dimers induce very flexible bends in DNA that are responsible for DNA compaction up to 50%. At higher HU concentrations, a rigid nucleoprotein filament is formed in which HU appears to arrange helically around the DNA without inducing significant condensation.
authors.affiliation: Molecular Biophysics, Kavli Institute of Nanoscience, Delft University of Technology, NL-2628 CJ, Delft, The Netherlands. noort@physics.leidenuniv.nl
authors.forename: John
authors.initials: J
authors.lastname: van Noort
authors.forename: Sander
authors.initials: S
authors.lastname: Verbrugge
authors.forename: Nora
authors.initials: N
authors.lastname: Goosen
authors.forename: Cees
authors.initials: C
authors.lastname: Dekker
authors.forename: Remus Thei
authors.initials: RT
authors.lastname: Dame
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D018625:Microscopy, Atomic Force
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C040330:histone-like protein HU, bacteria; D004247:DNA