title: The DNA of bacteriophage 643: isolation and properties of the DNA of a bacteriophage infecting lactic Streptococci.
abstract: The DNA extracted from bacteriophage 643, which infects group N strains of Streptococci, could be separated into four components by electrophoresis on agarose gels. Electron microscopy established the predominant form of the DNA to be a relaxed, circular molecule of molecular weight 14.9 X 10(6). The four species observed on electrophoresis are believed to be a circular monomeric form, a linear form derived from it, a circular dimeric form, and the corresponding linear dimer. Two DNA components were demonstrated by sedimentation velocity in the analytical ultracentrifuge and by zone sedimentation in sucrose gradients. These corresponded to a circular monomeric form and a circular dimeric form; no evidence for supercoiled forms was found by sedimentation in either neutral or denaturing solvents. Bacteriophage 643 DNA was sensitive to cleavage by single-strand-specific nuclease S1 and could be labeled in vitro by the PolI-catalyzed incorporation of [alpha-32P]dATP into the molecule under conditions that did not permit nick translation, suggesting that the circular duplex molecule is interrupted by a single-stranded gap.
mesh_terms: D001435:Bacteriophages / Q000235:genetics*; D001483:Base Sequence; D004262:DNA Restriction Enzymes; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D004279:DNA, Viral / Q000235:genetics / Q000302:isolation & purification*; D013294:Lactococcus lactis / Q000235:genetics*; D008854:Microscopy, Electron; D008970:Molecular Weight
chemical_list: D004269:DNA, Bacterial; D004279:DNA, Viral; D004262:DNA Restriction Enzymes