Figure 1.

Mapping of early-terminated transcripts in breakpoint cluster regions of MLL and MLL translocations partner genes A. Breakpoint cluster regions of the investigated genes MLL, AF4, AF9, ELL and ENL. Black boxes: exons separated by introns (black lines). Light grey horizontal bars: known breakpoint cluster regions (bcr's); numbers indicate exons flanking the individual bcr's. Grey vertical boxes: cryptic exons identified in this study. Triangles: identified cryptic poly-A sites in early-terminated transcripts. B. Real-time quantification of early-terminated transcripts. RNA transcripts derived from 10 healthy volunteers were reverse transcribed and equal amounts were mixed for analysis using three replicates. Full-length transcripts were set to 100% (black bars) and the relative amount of early-terminated transcripts is indicated (white bars). C. Early-terminated transcripts may arise by different mechanisms (artificial poly-adenylation; transcriptional pausing; DNA-damage-induced transcriptional stalling). In all these cases, the final exon carries an unsaturated splice donor site able to participate in splicing reactions. a) the unsaturated splice donor site initiates a splice reaction to a cryptic exons located in the downstream intron; b) the unsaturated splice donor site initiates a trans-splicing reaction into another transcript.