The Response of DNA Macromolecule to an Elongational Flow Field and Coil-Globule Transition of DNA

Abstract

It is known that large DNA molecules exhibit a conformational change between the coil and globule states with the addition of polyethylene glycol (PEG). We investigate the coil-globule transition of T4DNA by making use of the response of the molecule to a well-defined elongational flow field, where the response was monitored by the flow-induced birefringence. The flow-induced birefringence (Δn) increases with strain rate in elongational flow field -for the solutions of low PEG concentration indicating that the DNA molecule is in an expanded coil state. There are no Δn response at high PEG concentration solutions where the DNA molecule is in a well developed globule state. The dependence of Δn on PEG concentration accords with the PEG concentration dependence of DNA size which were directly measured by fluorescence micrograph method. Comparison of the flow birefringence and the fluorescence micrograph suggested that the globule of DNA molecule near the coil-globule transition point is soft and deformed by the elongational flow field though the well developed globule is rigid and in undeformed state. It is concluded that the elongational flow technique can be a useful method to investigate the coil-globule transition of large DNA molecules.