Characterization of bacteriophage S13 suN15 single-strand and replicative-form deoxyribonucleic acid.

The deoxyribonucleic acid (DNA) of bacteriophage S13 was shown to be single-stranded by the criteria of reactivity with formaldehyde, dependence of optical density on ionic strength, broad temperature-absorbance profile, and lack of molar equivalence of the purine and pyrimidine bases. The DNA has a molecular weight of 1.8 x 10(6) daltons, an S degrees (20) of 24.6 in SSC (0.15 m NaCl plus 0.015 m sodium citrate), and a buoyant density of 1.726 g/cc in CsCl. Electron microscopy showed the molecule to be circular. S13 replicative-form DNA was shown to be a double-stranded, circular molecule with a molecular weight of 3.5 x 10(6) daltons, an S([ill]) of 20.7 in SSC, and a buoyant density in CsCl of 1.710 g/cc. The finding that S13 DNA is slightly more pyrimidine-rich than phiX174 DNA but is indistinguishable by all other parameters supports the close genetic relationship between the two bacteriophages.