Summary
The his and nif genes of the Pl 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 concomintant 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 μm 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 μm 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.
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Communicated by F. Kaudewitz
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Pühler, A., Burkardt, H.J., Cannon, F.C. et al. Spontaneous degradation of pRD1 DNA into unique size classes is recA dependent. Molec. Gen. Genet. 171, 1–6 (1979). https://doi.org/10.1007/BF00274008
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DOI: https://doi.org/10.1007/BF00274008