Browsing by Subject "SEGMENTS"

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  • Eskelin, Katri Johanna; Poranen, Minna Marjetta (2018)
    Viruses protect their genomes by enclosing them into protein capsids that sometimes contain lipid bilayers that either reside above or below the protein layer. Controlled dissociation of virions provides important information on virion composition, interactions, and stoichiometry of virion components, as well as their possible role in virus life cycles. Dissociation of viruses can be achieved by using various chemicals, enzymatic treatments, and incubation conditions. Asymmetrical flow field-flow fractionation (AF4) is a gentle method where the separation is based on size. Here, we applied AF4 for controlled dissociation of enveloped bacteriophage phi 6. Our results indicate that AF4 can be used to assay the efficiency of the dissociation process and to purify functional subviral particles.
  • Lyytinen, Outi Leena; Starkova, Daria; Poranen, Minna Marjetta (2019)
    BackgroundCystoviruses have a phospholipid envelope around their nucleocapsid. Such a feature is unique among bacterial viruses (i.e., bacteriophages) and the mechanisms of virion envelopment within a bacterial host are largely unknown. The cystovirus Pseudomonas phage phi6 has an envelope that harbors five viral membrane proteins and phospholipids derived from the cytoplasmic membrane of its Gram-negative host. The phi6 major envelope protein P9 and the non-structural protein P12 are essential for the envelopment of its virions. Co-expression of P9 and P12 in a Pseudomonas host results in the formation of intracellular vesicles that are potential intermediates in the phi6 virion assembly pathway. This study evaluated the minimum requirements for the formation of phi6-specific vesicles and the possibility to localize P9-tagged heterologous proteins into such structures in Escherichia coli.ResultsUsing transmission electron microscopy, we detected membranous structures in the cytoplasm of E. coli cells expressing P9. The density of the P9-specific membrane fraction was lower (approximately 1.13g/cm(3) in sucrose) than the densities of the bacterial cytoplasmic and outer membrane fractions. A P9-GFP fusion protein was used to study the targeting of heterologous proteins into P9 vesicles. Production of the GFP-tagged P9 vesicles required P12, which protected the fusion protein against proteolytic cleavage. Isolated vesicles contained predominantly P9-GFP, suggesting selective incorporation of P9-tagged fusion proteins into the vesicles.ConclusionsOur results demonstrate that the phi6 major envelope protein P9 can trigger formation of cytoplasmic membrane structures in E. coli in the absence of any other viral protein. Intracellular membrane structures are rare in bacteria, thus making them ideal chasses for cell-based vesicle production. The possibility to locate heterologous proteins into the P9-lipid vesicles facilitates the production of vesicular structures with novel properties. Such products have potential use in biotechnology and biomedicine.
  • Casteras, Jean-Baptiste; Földes, Juraj (2020)
    We study singular radially symmetric solution to the Lin-Ni-Takagi equation for a supercritical power non-linearity in dimension N >= 3. It is shown that for any ball and any k >= 0, there is a singular solution that satisfies Neumann boundary condition and oscillates at leastktimes around the constant equilibrium. Moreover, we show that the Morse index of the singular solution is finite or infinite if the exponent is respectively larger or smaller than the Joseph-Lundgren exponent.