Studies on the properties of P1 site-specific recombination: evidence for topologically unlinked products following recombination

Cell. 1983 Apr;32(4):1301-11. doi: 10.1016/0092-8674(83)90311-2.


Bacteriophage P1 encodes its own site-specific recombination system consisting of a site at which recombination takes place called loxP and a recombinase called Cre. A number of lambda and plasmid substrates containing two loxP sites have been constructed. Using these substrates we have shown both in vivo and in vitro that a fully functional loxP site is composed of no more than 60 bp. In vitro, when an extract containing Cre is used, recombination between loxP sites on supercoiled, nicked-circle or linear DNA occurs efficiently. The most surprising result from the in vitro studies is that 50% of the products of recombination between loxP sites on a supercoiled DNA substrate are present as free supercoiled circles. The ability to produce free products starting with a supercoiled substrate suggests a rather unique property of Cre-mediated lox recombination, the implications of which are discussed in terms of possible effects of the protein on the topology of the DNA molecule.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacteriophage lambda / genetics
  • Coliphages / genetics*
  • DNA, Superhelical / genetics
  • DNA, Viral / genetics
  • Escherichia coli / genetics*
  • Genes, Viral*
  • Magnesium / pharmacology
  • Models, Genetic
  • Plasmids
  • Recombination, Genetic*
  • Spermidine / pharmacology


  • DNA, Superhelical
  • DNA, Viral
  • Magnesium
  • Spermidine