Site-specific recombinase, R, encoded by yeast plasmid pSR1

The R gene product (R protein) of Zygosaccharomyces rouxii plasmid pSR1 catalyzes site-specific recombination within a 58 base-pair (bp) sequence present in the 959 bp inverted repeats of this plasmid. The R protein was produced in Escherichia coli and partially purified. The partially purified protein catalyzed site-specific recombination in vitro without the supply of an energy source. Recombination resulted in intramolecular inversion or deletion, depending on whether the orientations of the two recombination sites on the substrate plasmid were the same or opposite. Presumably, R protein is the only protein required for the recombination reaction. A circular DNA molecule appears to be a better substrate than a linear molecule in R-mediated in vitro intramolecular recombination. The R protein binds to a set of six 12 bp elements within the inverted repeats of pSR1. Two of these 12 bp elements are arranged in an inverted configuration with a 7 bp spacer in the 58 bp sequence. The R protein mediates strand cleavage in vitro at the junction between the 12 bp elements and the 7 bp spacer. The cleavage sites on the top and bottom strands are staggered and flanked by polypurine tracts that form part of the 12 bp elements.