Studies will be carried out on DNA topoisomerases, DNA-dependent ATPases, and novel topological forms of DNA. The biological functions of topoisomerases will be studied by mutant isolation and specific inhibitor screening. Interactions between these enzymes and DNA will be studied in detail by the application of DNA sequencing techniques. The biochemistry of covalent bond formation between these enzymes and DNA will be deduced from the chemical identification of the bonds and mapping of the active sites. Interactions between DNA and a number of DNA-dependent ATPases will be studied at the DNA sequencing level, to elucidate the mechanisms by which these enzymes affect the secondary structure or tertiary supercoiling of DNA. The topology of segregation of DNA rings will be investigated. The preparation and characterization of double-stranded knotted DNA rings will be carried out, and the use of such substrates for studying the mechanisms of DNA topoisomerization will be explored.