title: Double-length, circular, single-stranded DNA from filamentous phage.
abstract: Wild-type and gene 3 mutant filamentous phage stocks, containing different relative amounts of multiple-length particles, were treated exhaustively with DNase and then were highly purified. The phage DNA was extracted and examined by electron microscopy. In all cases, about 0.03% of the molecules were circular dimers. (3)H-labeled phage DNA was separated as to size by sedimentation in a preformed CsCl density gradient. Individual fractions were then examined in the electron microscope, and the percentage of linear and circular monomer and dimer DNAs was determined. A peak of double-length, circular molecules (with the expected sedimentation constant of 38S) was found ahead of the 24S monomer peak. The double-length molecules had been purified 65-fold. As previously found for single-stranded DNA, the contour length of these molecules was strongly dependent upon ionic strength. Possible artifacts were ruled out, and it was shown that the double-length molecules arose from phage particles.
mesh_terms: D002499:Centrifugation, Density Gradient; D003090:Coliphages / Q000032:analysis*; D004267:DNA Viruses / Q000032:analysis; D004270:DNA, Circular / Q000302:isolation & purification*; D004277:DNA, Single-Stranded / Q000302:isolation & purification; D004279:DNA, Viral / Q000302:isolation & purification*; D004926:Escherichia coli; D008854:Microscopy, Electron; D014316:Tritium
chemical_list: D004270:DNA, Circular; D004277:DNA, Single-Stranded; D004279:DNA, Viral; D014316:Tritium