 Furthermore, these mutants have no supercoiling or connectivity requirements (Arnold et al., 1999) and have been shown to work in mammalian cells.Hyperactive resolvase mutants have so far proven useful in creating resolvases with altered sequence specificity but also in structural work.The entire resolvase recombination reaction can be reproduced "in vitro", requiring only resolvase, a substrate DNA and multivalent cations, using either wild type protein or hyperactive mutants.