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  • Title: Amplification in Escherichia coli of enzymes involved in genetic recombination: construction of hybrid ColE1 plasmids carrying the structural gene for exonuclease I.
    Author: Vapnek D, Alton NK, Bassett CL, Kushner SR.
    Journal: Proc Natl Acad Sci U S A; 1976 Oct; 73(10):3492-6. PubMed ID: 790387.
    Abstract:
    Endo-R-HindIII restriction endonuclease fragments obtained from F30 and pMB9 plasmid DNAs were ligated in vitro and used to transform a recB21 recC22 sbcB15 strain of E. coli K-12. The inability of this strain to stably maintain pMB9 alone permitted the isolation of transformants that carried hybrid plasmids containing the sbcB+ allele. These transformants became sensitive to ultraviolet light and recombination defieient and showed a 25-fold increase in the level of exonuclease I activity. The stability of the sbcB hybrid plasmids and their effects on exonuclease I activity have also been determined in wild-type and recA1 genetic backgrounds. The presence of the plasmids results in a 7-fold increase in the level of exonuclease I in a wild-type strain and 15-fold increase in a recA1 strain. The increased activity in the recA1 mutant appears to be a result of increased plasmid stability in this genetic background.
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