In addition to the standard type II enzyme known as DNA gyrase, we also found the ubiquitous presence of another cluster of DNA gyrase-like genes in eubacteria. Unlike the classical DNA gyrase, topoisomerase IV relaxes superhelical DNA in an ATP-dependent reaction but it is unable to introduce superhelical twists into closed circular DNA molecules. The topoisomerase IV genes are involved in the proper partitioning of newly replicated chromosomes into daughter cells. We are presently studying the biochemistry of gyrase and topoisomerase IV from a number of specialized eubacteria including Borrelia burgdorferi , the Lyme disease causative agent whose chromosome is uniquely linear, and B. subtilis where programmed cellular differentiation can occur. We are interested in the detailed examination of these structural relatedly, but functionally distinct, family of proteins in terms of their enzymology, sensitivity to specific antibiotics, cellular localization, regulation, and their interactions with other cellular components through biochemical and genetic means.
Bacteria can grow in extreme environments.
DNA gyrase and topoisomerase IV genes have also been identified in moderate and extreme thermophiles. We are currently examining the structure and function of these two sets of type II DNA topoisomerases in B. subtilis , B. stearothermophilus and B. caldolyticus. The comparative biochemical analysis will further provide a unique opportunity for understanding thermostability of this family of topoisomerases. The twelve linear and nine circular extrachromosomal DNAs of an infectious isolate of the Lyme disease spirochete Borrelia burgdorferi Molec. Sparfloxacin selects gyrase mutations in first-step Mycoplasma hominis mutants, whereas ofloxacin selects topoisomerase IV mutations.