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- Evilevitch, Alex, et al.
(author)
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Effects of salt concentrations and bending energy on the extent of ejection of phage genomes
- 2008
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In: Biophysical Journal. - : Elsevier BV. - 1542-0086 .- 0006-3495. ; 94:3, s. 1110-1120
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Journal article (peer-reviewed)abstract
- Recent work has shown that pressures inside dsDNA phage capsids can be as high as many tens of atmospheres; it is this pressure that is responsible for initiation of the delivery of phage genomes to host cells. The forces driving ejection of the genome have been shown to decrease monotonically as ejection proceeds, and hence to be strongly dependent on the genome length. Here we investigate the effects of ambient salts on the pressures inside phage-l, for the cases of mono-, di-, and tetravalent cations, and measure how the extent of ejection against a fixed osmotic pressure (mimicking the bacterial cytoplasm) varies with cation concentration. We find, for example, that the ejection fraction is halved in 30 mM Mg21 and is decreased by a factor of 10 upon addition of 1 mM spermine. These effects are calculated from a simple model of genome packaging, using DNA-DNA repulsion energies as determined independently from x-ray diffraction measurements on bulk DNA solutions. By comparing the measured ejection fractions with values implied from the bulk DNA solution data, we predict that the bending energy makes the d- spacings inside the capsid larger than those for bulk DNA at the same osmotic pressure.
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| 3. |
- Grayson, Paul, et al.
(author)
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The effect of genome length on ejection forces in bacteriophage lambda.
- 2006
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In: Virology. - : Elsevier BV. - 1096-0341 .- 0042-6822. ; 348:2, s. 430-436
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Journal article (peer-reviewed)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 λ, λb221cI26 and λcI60, which differ in genome length by 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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| 4. |
- Lindh, Roland, 1958-, et al.
(author)
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Approaches to the Tricritical Point in Quasibinary Fluid Mixtures
- 1984
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 52:10, s. 839-842
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Journal article (peer-reviewed)abstract
- When the Griffiths theory of tricritical points is extended to the eighth power of the order parameter, certain composition differences preserve the limiting behavior far from the tricritical point, an unexpected result that had been overlooked in earlier van der Waals model calculations. New calculations show that, along a path of constant tricritical composition and density and increasing temperature, a quasibinary system goes from two phases to one at the tricritical point, with no appearance of the third phase.
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