Double-Length, Circular, Single-Stranded DNA from Filamentous Phage |
| |
Authors: | Frances C Wheeler Rolf H Benzinger and Hermann Bujard |
| |
Institution: | Department of Biology, University of Virginia, Charlottesville, Virginia 22901;Institut fuer Genetik, Universitaet Heidelberg, Germany |
| |
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. |
| |
Keywords: | |
|
|