Formation of small circular DNA molecules via an in vitro site-specific recombination system.

The Cre-lox site-specific recombination system of bacteriophage P1 has been used to investigate the role of DNA flexibility in recombination. We have determined that a minimal distance of 82 bp must separate two loxP sites located on the same DNA molecule to allow these sites to undergo intramolecular recombination with one another. As a result of recombination, DNA circles as small as 116 bp have been produced. IN addition, we have demonstrated that the nuclease BAL 31 recognizes distortions in the DNA helix resulting from the formation of small DNA circles whose length is not a multiple of the helical repeat.