Polyacrylamide gel as a medium for DNA dissociation and reassociation

Several properties of thermal denaturation and renaturation of DNA in polyacrylamide gels were investigated: (1) Following electrophoresis the DNA band was scanned and shown to increase in absorbance with increasing temperature. The increase was proportioned to DNA concentration across the peak. (2) The dependence of the Tm on salt concentration over a hundred fold range was similar to that found for DNA in free solution. (3) Denaturation of several DNA samples ranging in G + C content from 26 to 71% was compared in gels and free solution. The relationship between Tm and % G + C was virtually identical for both sets of DNAs. (4) The kinetics of DNA renaturation in the gel was followed. Reassociation of bacteriophage T4 DNA was 2nd order and proceeded more rapidly in polyacrylamide gels than in free solution.