Angular Optical Trapping And Its Application To Dna Structures
DNA experiences constant mechanical stress in the cell, due to the action of enzymes and DNA-binding proteins. As a result, understanding the elastic properties and response to external stress is important in determining how DNA functions in vivo. Linear optical trapping has been employed previously to stretch DNA and measure its force-extension relationship. However, DNA is helical and is subject to winding, melting, and twisting during all parts of the cell cycle. Hence, measuring the response of DNA and DNA-based structures to torsional strain is equally (if not more) important. To this end, we have developed an angular optical trapping instrument which can detect and exert torque and twist, in addition to force and displacement. The torsional response of natural B-form DNA was studied, and an abrupt transition into a plectonemic state was observed for the first time. The Holliday junction, a fourway cruciform structure which is critical in DNA repair pathways, was also studied, and it was determined that this structure behaves like a nano-torque wrench, relieving torsional strain and promoting extensive branch migration events.
dissertation or thesis