Effects of the formation of the multistranded structure on electrophoretic mobility. DNA fragments (pSP64 DNA) with various sizes (300, 500, 900, and 1200 bp), were subjected to direct marking using a labeled probing oligonucleotide (probe 4; 60 bp) and a splint oligonucleotide (17 bp). As controls, the target DNA fragments were ³²P-labeled at the 5′-termini by T4 polynucleotide kinase and elecrophoresed in parallel. (Lanes 1,3,5,7) Results of autoradiographic patterns after direct marking; (lanes 2,4,6,8) ³²P-labeled target DNA fragments (indicated by arrowheads). (Lanes 1,2) 300-bp DNA fragment; (lanes 3,4) 500-bp DNA fragment; (lanes 5,6) 900-bp DNA fragment; (lanes 7,8) 1200-bp DNA fragment. For details, see Methods.