Speaker: E. Lynn Zechiedrich.
Title: DNA Knots.
Affiliation: Baylor College of Medicine.
Date: Friday, March 1, 2002.
Place and Time: Room 101 - Love Building, 3:35-4:35 pm.
Refreshments: Room 204 - Love Building, 3:00 pm.

Abstract. Knots occur in any long polymer. Considering that, for example, a bacterial cell must duplicate and segregate DNA that is about 1 millimeter in length within the confines of a microscopic cell, it is not surprising that knots are frequently found in DNA. We study the ubiquitous, essential topoisomerases, which break and pass DNA strands through each other to affect nearly every aspect of DNA metabolism. The bacterial enzymes are the cellular targets for many antibiotics, including the now-famous "Cipro" and the human enzymes are targets for many anticancer drugs. We have determined which of the four topoisomerases in bacteria untie DNA knots and links. We have characterized the types and frequency of knots that form naturally in cells. These are twist knots and the 3-noded twist occurs most frequently. Finally, we have determined that only a small increase in the amount of knots in cells prevents the function of an essential gene, which kills the cells.