Migration of hyperperiodic and control DNA in agarose gels. (a) Two-dimensional 4% NuSieve agarose gel electrophoresis of lambda DNA fragments (cut with NciI and PvuII) and (b) lambda fragments plus Ω4 fragments cut with the same restriction enzymes. Gels were run first at 4°C in the absence of intercalator (Ethidium Bromide, vertical) and then at 37°C in the presence of intercalator in the perpendicular direction (horizontal). The hyperperiodic Ω4 fragments (indicated by arrows) migrated more slowly than one would expect on the basis of its length. Similar anomalies were observed when using 2% agarose gels (data not shown). Gel electrophoresis on fragments SQ100 (185 bp, non-periodic, lane 3) and SQ322 (182 bp, hyperperiodic, lane 4) run at 37°C with EtBr (c) and at 4°C without EtBr (d). Lanes 1, 2, 5 and 6 correspond to 100 and 25 bp DNA ladders. At low temperature, the hyperperiodic fragment migrates more slowly than expected.