A DNA-binding domain swap converts the invertase Gin into a resolvase

DNA resolvases and invertases are closely related, yet catalyze recombinati on within two distinct nucleoprotein structures termed synaptosomes and inv ertasomes, respectively. Different protein-protein and protein DNA interact ions guide the assembly of each type of recombinogenic complex, as well as the subsequent activation of DNA strand exchange. Here we show that inverta se Gin catalyzes factor for inversion stimulation dependent inversion on is olated copies of sites I from ISXc5 res, which is typically utilized by the corresponding resolvase. The concomitant binding of Gin to sites I and III in res, however, inhibits recombination. A chimeric recombinase, composed of the catalytic domain of Gin and the DNA-binding domain of ISXc5 resolvas e, recombines two res with high efficiency. Gin must therefore contain resi dues proficient for both synaptosome formation and activation of strand exc hange. Surprisingly, this chimera is unable to assemble a productive invert asome; a result which implies a role for the C-terminal domain in invertaso me formation that goes beyond DNA binding. (C) 2000 Academic Press.