Abstract
Bacteria frequently need to adapt to altered environmental conditions. Adaptation requires changes in gene expression, often mediated by global regulators of transcription. The nucleoid-associated protein H-NS is a key global regulator in Gram-negative bacteria and is believed to be a crucial player in bacterial chromatin organization via its DNA-bridging activity. H-NS activity in vivo is modulated by physico-chemical factors (osmolarity, pH, temperature) and interaction partners. Mechanistically, it is unclear how functional modulation of H-NS by such factors is achieved. Here, we show that a diverse spectrum of H-NS modulators alter the DNA-bridging activity of H-NS. Changes in monovalent and divalent ion concentrations drive an abrupt switch between a bridging and non-bridging DNA-binding mode. Similarly, synergistic and antagonistic co-regulators modulate the DNA-bridging efficiency. Structural studies suggest a conserved mechanism: H-NS switches between a 'closed' and an 'open', bridging competent, conformation driven by environmental cues and interaction partners.
Highlights
The bacterial genome is compacted by a vast variety of factors, including DNA supercoiling, and macromolecular crowding, it owes much of its organization to nucleoid-associated proteins (Dame, 2005; Dame et al, 2011; Dillon and Dorman, 2010; Dorman, 2013; Rimsky and Travers, 2011; Travers and Muskhelishvili, 2005; Luijsterburg et al, 2008; Dame and Tark-Dame, 2016)
Genome-wide binding studies have revealed that Histone-like Nucleoid Structuring protein (H-NS) binds along the genome in long patches (Grainger et al, 2006; Kahramanoglou et al, 2011; Lucchini et al, 2006; Navarre, 2006; Oshima et al, 2006), which have been proposed to mediate the formation of genomic loops (Noom et al, 2007; van der Valk et al, 2014)
The DNA-bridging assay relies on immobilization of bait DNA on magnetic microparticles and the capture and detection of 32P labeled prey DNA if DNA-DNA bridge formation occurs. 80% of initial prey DNA is recovered at high H-NS concentrations
Summary
The bacterial genome is compacted by a vast variety of factors, including DNA supercoiling, and macromolecular crowding, it owes much of its organization to nucleoid-associated proteins (Dame, 2005; Dame et al, 2011; Dillon and Dorman, 2010; Dorman, 2013; Rimsky and Travers, 2011; Travers and Muskhelishvili, 2005; Luijsterburg et al, 2008; Dame and Tark-Dame, 2016). H-NS is an important regulator of global gene expression, implied in mediating global transcriptional responses to environmental stimuli (osmolarity, pH, temperature) (Atlung and Ingmer, 1997), and operating as xenogeneic silencer, silencing horizontally integrated DNA (Navarre et al, 2006). H-NS operation is modulated by environmental stimuli and through interplay with other proteins (Atlung and Ingmer, 1997; Stoebel et al, 2008). H-NS consists of three structural domains: a C-terminal domain responsible for DNA binding (Shindo et al, 1995), a N-terminal van der Valk et al eLife 2017;6:e27369.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
