Chromosomal translocations causederegulated BCL6expression bypromotersubstitution inBcell lymphoma

summary, our analysis of the 5' terminus of BCL6RNA indicated that in all three NHL cases the der(3) chromosome expressed Ig-BCL6 chimeric transcripts initiated within the IgH locus, most commonly at the I promoters and spliced to BCL6 exon 2 sequences. Allthese transcripts retained an intact BCL6 coding domain.The chimeric, butnotthenormal, BCL6 allele is transcribedin Ly8 cellsTo gain further insight into the structure and pattern of expression of the various BCL6 mRNA species in NHLwith t(3;14), we analyzedBCL6mRNAin Ly8cells using RNase protection assays. First, we tested whether Ly8 cells expressed a BCL6 RNA lacking exon 1 sequences,as predicted by the RACEproduct shown in Figure 3.Previous RNase protection and cDNA cloning studies have shown that BCL6transcription is normally initiated from a major(Pb) promoter, active in all cells tested, and an upstream minor (Pa) promoter, active in only some Bcelllines (data not shown).Representativeresults inFigure4Ademonstratethat with