Excision of prophage lambda in a cell-free system.

A cell-free system that promotes the excision of prophage lambda DNA has been established. The substrate for the reaction is phage DNA carrying two attachment sites, which, in vivo, undergoes intramolecular recombination between these sites. The in vitro recombination system is efficient; 25-35% of the substrate DNA undergoes recombination in 30 min. There is an absolute requirement for ATP; Mg++ and spermidine are stimulatory. RNA does not appear to be involved, nor can a role for DNA synthesis be demonstrated.