Isolation of an ITD mutation-containing amplicon with a very small peak height. A: PCR products subjected to capillary electrophoresis demonstrated dominant 330-base wild-type amplicons and minute amounts of a 426-base mutation-bearing ITD amplicon (arrow) with a peak height of 110 RFUs. The reconfigured gel block was installed at 30 minutes. Four tubes were collected at 1-minute intervals. B: A predominant 426-base peak was amplified from the second collection tube. ITD peaks are blue shaded, and size standard peaks are red shaded. x axis, size in bases. y axis, RFUs. C: Ethidium bromide-stained polyacrylamide gel (10%) electrophoresis. Lane 1, germline amplicon of Flt3 gene (330 bases, arrow) and undetected ITD mutation (426 bases with a peak height of 110 RFUs in A). Lane 2, 50-bp DNA ladder (Invitrogen, Carlsbad, CA). Sequencing of the PCR products before fraction collection (D) and after fraction collection and reamplification of the amplicon with the ITD mutation (E). Arrow indicates the insertion site of the ITD.