BACTERIOPHAGES OF STREPTOCOCCUS-PNEUMONIAE - PHYSICOCHEMICAL PROPERTIES OF BACTERIOPHAGE-DP-4 AND ITS TRANSFECTING DNA

The properties of Dp‐4 phage and its DNA have been studied. The phage has a polyhedral head of 60 nm diameter, a tail 155 nm long and a buoyant density in CsCl of 1.48 g/cm3. Analysis by acrylamide gel electrophoresis indicates the presence of five polypeptides. Dp‐4 DNA has a molecular weight of 37 * 106, a melting point of 83.5°C (when dissolved in 0.15 M NaCl/0.015 M sodium citrate, pH 7.0) and a G + C content of about 33%. Denaturation of DNA yields two strands of different buoyant density in a neutral CsCl gradient. The interaction of poly(U,G) with the heavy strand strongly enhances its density and allows the preparative separation of both strands. Native Dp‐4 DNA has unusual physical properties: abnormally low buoyant densities both in CsCl (1.666 g/cm3) and in Cs2SO4 (1.410 g/cm3) (which do not correspond to the value predictable from the G + C content of the DNA), and a high thermal stability at low ionic strength. Copyright © 1979, Wiley Blackwell. All rights reserved