 Wild type resolvase system absolutely requires a supercoiled substrate and that the recombination sites are oriented in a direct repeat on the same DNA molecule.However, a number of "deregulated" or "hyperactive" mutants that have lost the requirement for the accessory sites have been isolated.These mutants are capable of catalysing recombination between two copies of site I only, which basically reduces the recombination site size from 114bp to only 28bp.