Figure 7.

Inhibition of Int by EDTA can be prevented by addition of one of the recombination substrates. Int (400 nM) was incubated for 60 min with or without EDTA and with or without a protecting 50-mer att site (200 nM). Int activity was then measured by addition of a partner att site encoded on a plasmid (attP; pRT702, attB; pRT600) and in reactions that contained no att site during pre-incubation, a 50-mer att site. The recombination reactions were incubated (30°C, 1 h) and the products of recombination were analysed after digestion with ScaI. The substrates pRT702 (2491 bp; black arrow) or pRT600 (3035 bp; grey arrow) are each cut once by ScaI but if they have undergone recombination with their partner att sites contained on the 50-mers, the linear products are cleaved to give 1671 and 869 bp (pRT702; black arrowheads) and 1887 and 1200 bp (pRT600; grey arrowheads). M are molecular weight markers. The lower panel shows that inhibition by EDTA could be prevented if ZnSO₄ (final concentration 0.5 mM) is added at the start of pre-incubation.