Representative analysis of RT-PCR amplification of the TEL/AML1 chimeric transcripts in t(12; 21) ALL samples. (A) The relative position of the primers used to amplify the TEL/AML1 fusion cDNAs resulting from the most common breakpoint within the TEL gene (TEL bp-2) and the one occuring at a more 5′ site (TEL bp-1) is shown. The amplified fragment in the lane corresponding to patient n.1 is slighty shorter than usual (as in case n.2), lacking the 39 bp-AML1 exon 2. The sequence analysis of the cDNA product obtained from patient n.3, showed the junction of the exon 4 of the TEL gene to exon 2 of the AML1 gene.