tokens: When cells were microinjected with TFOs designed to bind to a 30-bp polypurine site situated between the two TK genes , recombination was observed at frequencies in the range of 1 % , 2,500-fold above the background .
folded_tokens: when cell be microinject with tfo design to bind to a 30-bp polypurine site situate between the two tk gene , recombination be observe at frequency in the range of 1 % , 2,500-fold above the background .