Bacterial DNA gyrase catalyzes ATP-dependent negative supercoiling of plasmid and chromosomal DNA. The GyrA and GyrB subunits that make up a tetramer subunit enzyme are essential in many bacteria and are important chemotherapeutic targets for treating pathogenic bacterial infection. DNA replication, RNA transcription, homologous recombination, site-specific recombination, gene transposition, and chromosome condensation are all influenced by negative supercoil density. E. coli and Salmonella Typhimurium are the most thoroughly studied organisms from a supercoil dynamics perspective. They share a conserved chromosomal gene order and have highly conserved homologous proteins involved in DNA replication regulation of transcription and DNA topology. Nonetheless, E. coli maintains plasmid and chromosomal DNA at a significantly (15%) higher supercoil density than Salmonella. E. coli is actually addicted to high supercoiling since it stops growth and cell division when the chromosomal DNA supercoiling falls by 15%, i.e. down to the level of WT Salmonella. Surprisingly, Salmonella can carry out well ordered DNA replication and cell division cycles in cells that lack all diffusible negative supercoils. Moreover, different phenotypes for identical mutations in GyrA, GyrB, and the MukBEF DNA condensin as well many other proteins prove that highly conserved proteins have evolved different roles in “core biochemistry” directing gene expression and chromosome dynamics in each species. Some implications of species divergence and a tool box of genetic modules designed to measuring in vivo bacterial supercoil density and transcription elongation rates around the genome will be presented.


N. Patrick Higgins (b. 1946) completed undergraduate studies at Wichita State University in 1969 and earned a Master’s degree in Biology in 1970. He was drafted and then in 1972 started his Ph.D. degree in the Department of Microbiology at the University of Chicago graduating 1976 for work with Dr. Bernard Strauss in the Department of Microbiology. They published a model for error free DNA repair that predicted replication fork reversal, which has been confirmed in both bacterial and mammalian DNA repair systems. He continued work at the U of Chicago in the Department of Biochemistry as a postdoc in Nicholas Cozzarelli’s lab where he was first to purify two subunits of DNA gyrase and reconstitute the enzyme in vitro. This work prove which subunits were targets of two important drugs, novobiocin and nalidixic acid. In 1979 he joined the faculty of the University of Wyoming and established a collaboration with Toto Olivera at the University of Utah. Together they were first to analyze the mechanism of bacteriophage Mu transposition in vitro with biochemical and molecular biology techniques. After moving to Birmingham in 1984 to the Department of Biochemistry , he was promoted to Associate Professor in 1985 and made a full Professor in 1991. In 2001 he was the E. A. Watkins Visiting Professor at his alma mater Wichita State University. He was also a co-director with Dr. Lisa Guay-Woodford of the new Heflin Center for Human Genetics in the Medical School serving to 2009. He directed the UAB Fermentation Facility from 2000 – 2014, and currently holds the rank of Professor Emeritus of Biochemistry and Molecular Genetics at the University of Alabama at Birmingham. He remains active in his lab.