Separation of the complementary strands of DNA fragments on polyacrylamide gels

32P-labeled (in vivo) phiX174 RFI DNA was restricted by Hinc II. Three aliquots of the same digest: a) nondenatured, b) heat denatured, and c) denatured by 5 mM Me-HgOH were analyzed on 3-15% acrylamide gel gradients or on 3% gels with reduced N,N'-methylene-bis-acrylamide. The autoradiography of the gels showed that the nondenatured sample migrates two times faster than the denatured samples. After denaturation each original fragment appeared as a doublet. Using in vitro synthesized RFI DNA labeled only in negative strand with 32P we could identify the position of the negative strand in each denatured doublet. The single strand DNA fragments could be recovered from the gel slices on a semi-preparative scale by electrophoresis into dialysis tubing.