All ETDs from UAB

Advisory Committee Chair

Norman P Higgins

Advisory Committee Members

David E Graves

Janet L Yother

Dmitry G Vassylyev

Kirill M Popov

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine


Gyrase introduces negative supercoils into bacterial DNA. In balance with topoisomerase I, it contributes to the maintenance of constant negative DNA supercoiling. It was shown that in Escherichia coli negative supercoil density of pBR322 plasmid is higher than in Salmonella typhimurium. One of the possible explanations of this phenomenon is a difference of DNA gyrase activity between E. coli and S. typhimurium. We developed in vitro assay of gyrase activity which has shown that DNA gyrases of E. coli and S. typhimurium have the same supercoiling end point, but E. coli gyrase works slightly faster than the S. typhimurium enzyme. To see how this rate difference influences supercoiling on the chromosome, the in vivo assay based on excision of sequence surrounded by resolvase sites has been used in various strains. The efficiency of resolvase action correlates with supercoiling density at the resolvase sites. This assay has shown that E. coli gyrB does not significantly influence supercoiling density, but E. coli gyrA relaxes the S. typhimurium chromosome. This fact can be explained by inefficient interaction of E. coli GyrA with S. typhimurium DNA.