Heat denaturation of P2 bacteriophage DNA: Compositional heterogeneity☆

摘要: Abstract DNA extracted from the Escherichia coli bacteriophage P2, as studied in electron microscope, consists of linear monomers uniform length (13.1 to 13.2 μ, corresponding a molecular weight 2.2 × 107), addition dimers and circles. These disappear when temperature is raised just above that at which denaturation begins. The presence P2 cohesive ends like those described for phage λ thus confirmed. A direct comparison with high infectivity recovered, both show are much more stable heat than λ. Electron microscopy partially denatured reveals several highly characteristic zones along “melting map”, recognizable by they start denaturing. Changes ultraviolet absorption 260 nm wavelength during (melting curves), also accompanying spectral changes, indicate contains least three fractions different base pair contents (fraction I: 20% mass 34% (G + C) content; II: 16% 45% C); III: 64% 58% C). microscopical observations permit one conclude this compositional heterogeneity intra-molecular. correlation between defined melting curves map tentatively established. Hy, believed be genetically identical except small segment its chromosome, appears fraction I over-represented Hy DNA. microscopic data compatible finding, but effect very small. On basis it possible localize on genetic region differentiates thereby orient physical respect representation chromosome.