Mutational analysis of the BCL6 first intron and non-coding exon 1 in gastric lymphoma. (A) Distribution of somatic mutations in the BCL6 hypermutation region (nucleotides +358 to +1148 corresponding to the first transcription start site) covering MMC located at 5′ of the first intron detected in 24 cases of gastric lymphoma. The abscissa represents the position along the MMC region, starting from the first nucleotide of BCL6 non-coding exon 1. The ordinates correspond to the number of cases with somatic mutations at each position. Black bars indicate the number of cases with somatic mutations. Constitutional single-nucleotide polymorphisms (SNPs) were not counted. BCL6 translocation breakpoints within this region are indicated below the graph. • indicates the translocation breakpoints overlapping with somatic mutations detected; ○ indicates the translocation breakpoints not overlapping with somatic mutations detected. (B) BCL6-deregulating mutations in the two BCL6 binding motifs (BSE1A and BSE1B) located within the non-coding exon 1 of the gene detected in 8 cases of gastric lymphoma. The positions of the two BCL6 binding motifs are indicated above the case no. 1. The mutated nucleotides are underlined with the wild-type sequences shown below. *DLCLML cases.