My research covers a number of aspects of DNA topology and its modulation by topoisomerases. DNA topology, including supercoiling and catenation of DNA, is implicated in all DNA-related processes in vivo, including replication, transcription and recombination. My interests range from the probing of the structure and energetics of supercoiled DNA to the mechanism and function of type II topoisomerases, essential enzymes which modulate DNA topology. The enzymes are important antibacterial and anticancer drug targets.
Supercoiled DNA has a high torsional energy. This energy has the potential in vivo to untwist the DNA helix, and drives the initiation of processes which require the unwinding of DNA, for example replication and transcription initiation. We are investigating the energetics of supercoiled DNA through binding studies of the DNA intercalator ethidium bromide, and using a model recombination system (loxP -Cre) as a probe of the conformation of supercoiled DNA.
E. coli DNA gyrase introduces negative supercoiling into DNA using the free energy of ATP hydrolysis, and is responsible for the maintenance of negative supercoiling in the cell, and the removal of positive supercoiling ahead of transcription and replication complexes. Topoisomerase IV is a homologous enzyme, which is implicated in the decatenation of daughter chromosomes and plasmids following replication. We are pursuing mechanistic investigations of these enzymes, focusing in particular on the coupling of ATP binding and hydrolysis to the DNA-processing step. We are also studying the site and mode of action of the enzymes in vivo.