Identification of fusion transcripts by RT-PCR. Primers used were MLL-7S and p300-8A (lane 1), MLL-9S and p300-7.5A (lane 2), and p300-2S and MLL-11A (lane 3), respectively. Sequencing analysis of the amplified fragment (lane 1) showed a 344-bp fragment of MLL exons 7 through 9 in the 5′ region and 524 bp of p300 exon in the 3′ region. Primers (p300-2S and MLL-11A) were designed for the detection of reciprocal p300-MLL transcript, resulting in the detection of amplified fragment (lane 3).