title: Ionic switch controls the DNA state in phage λ.
abstract: We have recently found that DNA packaged in phage λ undergoes a disordering transition triggered by temperature, which results in increased genome mobility. This solid-to-fluid like DNA transition markedly increases the number of infectious λ particles facilitating infection. However, the structural transition strongly depends on temperature and ionic conditions in the surrounding medium. Using titration microcalorimetry combined with solution X-ray scattering, we mapped both energetic and structural changes associated with transition of the encapsidated λ-DNA. Packaged DNA needs to reach a critical stress level in order for transition to occur. We varied the stress on DNA in the capsid by changing the temperature, packaged DNA length and ionic conditions. We found striking evidence that the intracapsid DNA transition is 'switched on' at the ionic conditions mimicking those in vivo and also at the physiologic temperature of infection at 37°C. This ion regulated on-off switch of packaged DNA mobility in turn affects viral replication. These results suggest a remarkable adaptation of phage λ to the environment of its host bacteria in the human gut. The metastable DNA state in the capsid provides a new paradigm for the physical evolution of viruses.
authors.affiliation: Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
authors.forename: Dong
authors.initials: D
authors.lastname: Li
authors.affiliation: Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
authors.forename: Ting
authors.initials: T
authors.lastname: Liu
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Zuo
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Tao
authors.initials: T
authors.lastname: Li
authors.affiliation: Department of Physics, The George Washington University, Washington, DC 20052, USA.
authors.forename: Xiangyun
authors.initials: X
authors.lastname: Qiu
authors.affiliation: Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA Department of Biochemistry and Structural Biology, Lund University, SE-221 00 Lund, Sweden alexe@cmu.edu.
authors.forename: Alex
authors.initials: A
authors.lastname: Evilevitch
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics*; D002213:Capsid / Q000737:chemistry; D042003:DNA Packaging; D004279:DNA, Viral / Q000737:chemistry*; D016679:Genome, Viral; D009994:Osmolar Concentration; D013696:Temperature
chemical_list: D004279:DNA, Viral