The prokaryotic beta-recombinase catalyzes site-specific recombination in mammalian cells

The development of new strategies for the in vivo modification of eukaryoti c genomes has become an important objective of current research. Site-speci fic recombination has proven useful, as it allows controlled manipulation o f murine, plant, and yeast genomes, Here we provide the first evidence that the prokaryotic site-specific recombinase (beta-recombinase), which cataly zes only intramolecular recombination, is active in eukaryotic environments . beta-Recombinase, encoded by the beta gene of the Gram-positive broad hos t range plasmid pSM19035, has been functionally expressed in eukaryotic cel l lines, demonstrating high avidity for the nuclear compartment and forming a clear speckled pattern when assayed by indirect immunofluorescence, In s imian COS-1 cells, transient beta-recombinase expression promoted deletion of a DNA fragment lying between two directly oriented specific recognition/ crossing over sequences (six sites) located as an extrachromosomal DNA subs trate. The same result was obtained in a recombination-dependent lacZ activ ation system tested in a cell Line that stably expresses the beta-recombina se protein. In stable NIH/3T3 clones bearing different number of copies of the target sequences integrated at distinct chromosomal locations, transien t beta-recombinase expression also promoted deletion of the intervening DNA , independently of the insertion position of the target sequences. The util ity of this new recombination tool for the manipulation of eukaryotic genom es, used either alone or in combination with the other recombination system s currently in use, is discussed.