the American Academy of Arts and Sciences and the American Philosophical Society. Throughout the course of Susan's career, she has been published over 250 times. Taxol mechanism discovery Horwitz had been working on several anti tumor drugs in her lab that inhibited the cell cycle by binding to DNA. The National Cancer Institute (NCI) contacted her one day in 1977, and inquired whether she would be interested in working on a drug for them, called Taxol. This was a drug that had been obtained from the yew plant Taxus brevifolia. At the time there was only one published article about the drug from 1971. Horwitz happily complied to the offer and received 10 milligrams of the drug from the NCI. She planned to examine the drug with her graduate student, Peter Schiff, for a month. After the month was up, they planned to decide whether or not the project displayed enough promise to continue. By the end of the month, they were heavily invested in the drug due to its outstanding uniqueness. They had discovered that the molecule acted by interacting with microtubules. They performed assays with the molecule to determine what cell cycle phase was arrested by its mechanism of action. The stoppage of the cycle turned out to clearly occur during mitosis. With this realization, they quickly discovered that there was a binding site for the molecule located on the tubulin, which led them to their next discovery that the microtubules were frozen in place when the molecule was bound in this site. The cytoskeleton was essentially stuck in place, which served to inhibit any depolymerization. Their next step in the process was to identify where the binding site was and how the molecule managed to bind effectively. At this point, Horwitz enlisted another colleague, George Orr, to aid in the work. They used photo-affinity analogues to identify putative regions of interaction between the molecule and tubulin. Obtaining these analogues was an arduous task for the team; however, after some time, suitable analogues were synthesized and successfully used in their studies to identify regions of interaction between Taxol and ß-tubulin. Electron crystallography studies from other scientists including Eva Nogales and Ken Downing at the Lawrence Berkeley lab in California, confirmed their initial findings, and following a period of extensive investigation, the binding site for Taxol on ß-tubulin was officially delineated. This revolutionary discovery initiated the search for similar