The block copolymer Pluronic F127 and water form a gel-like cubic phase which is useful as sieving media for electrophoretic separation of DNA fragments in capillary electrophoresis because, below a transition temperature of 11 degreesC, the gel melts to an easily handled liquid solution. Here we study the conformational state and the mode of electrophoretic migration of double stranded DNA in the cubic gel. The DNA remains in B form in the Pluronic F127 gel and functions as a substrate for PCR, and there is no detectable effect on the Pluronic solution-gel transition temperature by the presence of DNA of concentrations up to the overlap concentration. Velocity and coil deformation measurements during electrophoresis show that the mode of DNA migration in this gel is qualitatively different compared to conventional gels. DNA coils are deformed with the helix axis preferentially perpendicular to the field direction, and the electrophoretic mobility varies discontinuously with field strength. At low field strengths (below 11 V/cm in a 30% gel) we find further support for the hypothesis that migration occurs along grain boundaries between crystal domains (Svingen et al. Langmuir 2002,18, 8616-8619). This mode of migration is general since it occurs for DNA between 200 and 5400 base pairs (bp) and at gel concentrations between 25 and 30%, and we show that it requires the cubic phase and is not due to the high polymer concentration as such. At about 11 V/cm the electrophoretic mobility of ds DNA increases discontinuously because of reduced friction. We propose that the cause is a reversible perturbation of the cubic structure induced by DNA when migrating at the stronger electric fields.