title: Spontaneous degradation of pRD1 DNA into unique size classes is recA dependent.
abstract: The his and nif genes of the P1 type plasmid pRD1 were lost at a high frequency in a recA+ but not in a recA- Escherichia coli host during growth in a non-selective medium. 92% of the His- Nif- segregants after 6 subcultures retained the genetic markers of the precursor plasmid RP4, while the remainder lost all of the pRD1 markers with the concomitant loss of ccc-DNA. Plasmids purified from the His- Nif- segregants resembled RP4 in the physical and genetic properties examined. The contour length of pRD1 DNA molecules from a recA- strain was 49 micrometer corresponding to a molecular weight of 101 Mdals and the buoyant density was 1.715 g/cm3. In contrast, the contour lengths of plasmid molecules isolated from a recA+ host carrying pRD1 fell into 3 size classes of 49, 19 and 2 micrometer corresponding to molecular weights of 101, 39 and 4 Mdals respectively and two DNA species of buoyant density 1.715 and 1.719 g/cm3 were observed.
mesh_terms: D004269:DNA, Bacterial / Q000235:genetics*; D004274:DNA, Recombinant; D004926:Escherichia coli / Q000235:genetics*; D005796:Genes; D007711:Klebsiella pneumoniae / Q000235:genetics*; D008970:Molecular Weight; D009154:Mutation; D010957:Plasmids; D011995:Recombination, Genetic
chemical_list: D004269:DNA, Bacterial; D004274:DNA, Recombinant