Spontaneous degradation of pRD1 DNA into unique size classes is recA dependent
✍ Scribed by Pühler, A. ;Burkardt, H. J. ;Cannon, F. C. ;Wohlleben, W.
- Book ID
- 104697403
- Publisher
- Springer
- Year
- 1979
- Tongue
- English
- Weight
- 507 KB
- Volume
- 171
- Category
- Article
- ISSN
- 0026-8925
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✦ Synopsis
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.