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The effect of genome length on ejection forces in bacteriophage lambda

Department of Physics, California Institute of Technology, Pasadena, 91125, USA.
Virology (Impact Factor: 3.28). 06/2006; 348(2):430-6. DOI: 10.1016/j.virol.2006.01.003
Source: PubMed

ABSTRACT A variety of viruses tightly pack their genetic material into protein capsids that are barely large enough to enclose the genome. In particular, in bacteriophages, forces as high as 60 pN are encountered during packaging and ejection, produced by DNA bending elasticity and self-interactions. The high forces are believed to be important for the ejection process, though the extent of their involvement is not yet clear. As a result, there is a need for quantitative models and experiments that reveal the nature of the forces relevant to DNA ejection. Here, we report measurements of the ejection forces for two different mutants of bacteriophage lambda, lambdab221cI26 and lambdacI60, which differ in genome length by approximately 30%. As expected for a force-driven ejection mechanism, the osmotic pressure at which DNA release is completely inhibited varies with the genome length: we find inhibition pressures of 15 atm and 25 atm, for the short and long genomes, respectively, values that are in agreement with our theoretical calculations.

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    • "The force driving ejection of the protein from P22 arises from the confined DNA and is expected to be similar to that associated with the ejection of DNA from λ phage , which like P22 has a T¼ 7 capsid and is about the same size . Grayson et al . ( 2006 ) carried out osmotic suppression measurements on λ for the 48 . 5 kb wild - type genome and a 37 . 7 kb mutant and found that the ejection was completely inhibited at pressures of 20 – 25 and 10 – 15 atm , respectively . The pressure required to inhibit the E proteins that we have observed for P22 originates from 43 . 5 kb - length of "
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    ABSTRACT: Double-stranded DNA bacteriophages are highly pressurized, providing a force driving ejection of a significant fraction of the genome from its capsid. In P22-like Podoviridae, internal proteins ("E proteins") are packaged into the capsid along with the genome, and without them the virus is not infectious. However, little is known about how and when these proteins come out of the virus. We employed an in vitro osmotic suppression system with high-molecular-weight polyethylene glycol to study P22 E protein release. While slow ejection of the DNA can be triggered by lipopolysaccharide (LPS), the rate is significantly enhanced by the membrane protein OmpA from Salmonella. In contrast, E proteins are not ejected unless both OmpA and LPS are present and their ejection when OmpA is present is largely complete before any genome is ejected, suggesting that E proteins play a key role in the early stage of transferring P22 DNA into the host. Copyright © 2015 Elsevier Inc. All rights reserved.
    Virology 07/2015; 485:128-134. DOI:10.1016/j.virol.2015.07.006 · 3.28 Impact Factor
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    • "In the in vitro λ experiments [36] [37] [38] [39], phage virions are immersed in a solution containing PEG and/or DNA condensing agents, and DNA is ejected when triggered by the LamB receptor protein. "
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    Physical Biology 12/2010; 7(4):045006. DOI:10.1088/1478-3975/7/4/045006 · 3.14 Impact Factor
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    • "The first group of studies uses a continuum representation of DNA and the apparatus of statistical mechanics. These methods have been able to reflect the basic physics of DNA confinement and to estimate thermodynamic properties such as forces and free energy (Grayson et al., 2006; Kindt et al., 2001; Purohit et al., 2003; Purohit et al., 2005; Tzlil et al., 2003). The continuum approach has also been successful in explaining the role of the osmotic pressure during genome ejection (Evilevitch et al., 2008). "
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