Neuroblastoma double minutes isolated by pulsed-field gel electrophoresis without prior strand-cleaving treatments.

In a human neuroblastoma line, minute chromosomes were separable from the bulk of interphase nuclear DNA by contour-clamped homogeneous electric field (CHEF) gel electrophoresis. The minute chromosomes showed a homogeneous size of approximately 3 Mbp and contained amplified N-myc genes. Fractionation was accomplished without prior strand-cleaving treatment of the DNA, indicating that at least a portion of the minute chromosomes exist as free entities in the interphase nuclei. Human alphoid satellite DNA sequences were also detected in the 3-Mbp band. It is possible that alphoid sequences are contained in the constricted central region that joins these double minutes.