Reversibility of DNA loops exit during single cell gel electrophoresis

Abstract

The kinetics of DNA exit during single cell gel electrophoresis (comet assay) of human lymphocytes has been investigated. The electrophoresis was carried out at neutral pH either in the absence or in the presence of different ethidium bromide concentrations. The demonstrated dependence of the DNA exit efficiency on the ethidium bromide concentration indicates that the comet tail consists of DNA loop domains extended by the electric field. The loop exit is essentially favored when the DNA torsional constraint is relaxed. In contrast, the comet disappearance after the switching off the electric field was observed if some level of the constraint remained in the extended loops. Several possibilities of applications of the revealed effects for improvement of the comet assay are discussed.