Regularity between Phase Transfer and Conformation of Single DNA Molecules in Aqueous Two-Phase System Measured by In Situ Fluorescence Microscopy

Abstract

We found the regularity between phase transfers and the conformations of single giant linear double-stranded deoxyribonucleic acid (DNA; λDNA and T4GT7DNA) molecules in the aqueous two-phase system (ATPS) containing 4.0% polyethylene glycol (PEG), 7.4% dextran, and 0 – 20 mM (1 M = 1 mol dm⁻³) Mg²⁺ by in situ fluorescence microscopy. The DNAs tended to show a conformational change from an elongated random-coil state to a compacted globule state with an increase in the PEG and Mg²⁺ concentrations. The random-coiled DNAs underwent phase transfer across the ATPS interface from the PEG-rich top phase to the dextran-rich (PEG-poor) bottom phase, and vice versa. The globular DNAs were trapped at the ATPS interface and were not detached. In addition, the conformational change of the DNAs from the globule state to the random-coil state occurred at the ATPS interface at 6 – 9 mM Mg²⁺. The conformational change of the shorter DNA (λDNA) at the ATPS interface took less time than that of the longer DNA (T4GT7DNA).