Host protein requirements for in vitro site-specific DNA inversion.

Flagellar phase variation is mediated by a recombination event that occurs at specific sites leading to inversion of a chromosomal segment of DNA. The presence of a 60 bp recombinational enhancer sequence on the DNA substrate molecule results in a 150-fold stimulation in the initial rate of inversion. The protein components required for inversion have been purified. They include the 21,000 dalton recombinase (Hin), a 12,000 dalton host protein (Factor II), and one of the major histone-like proteins of E. coli HU. The dependence of the initial rate of recombination on HU varies with respect to the location of the recombinational enhancer. The role of HU, Factor II, and the enhancer in facilitating site-specific recombination is discussed.