Mapping the deregulating mutations.

Transient transfection assays were performed as described in Figure 1, using the reporter constructs shown on the left of each panel. Grey fragments correspond to the mutated 5′ flanking, exon 1 (box), and intron 1 region of the original allele (construct “a”), which were swapped in all possible combinations to map the deregulating mutation(s). Asterisks indicate the presence of mutations (note that 2 distinct nucleotide changes were present in the exon 1 sequences of allele 93-611A, 93-611B, and 93-2889A). Bars represent the activities of the resultant constructs (mean ± SD), obtained from 2 independent experiments performed in duplicate. In all 4 cases, a single mutation located in the BCL6 first noncoding exon recapitulates the activity displayed by the original construct.