Chromosome translocation activates heterogeneously initiated, bipolar transcription of a mouse c‐myc gene.

In many mouse plasmacytomas, the active c‐myc gene has been truncated by chromosome translocation with the resultant severance of the protein‐coding sequence from the normal promoter. Transcripts of such truncated c‐myc genes were analyzed by Northern blotting, nuclease S1 mapping, primer extension assays and cDNA cloning. We conclude that transcription originates from multiple initiation sites on both c‐myc coding and non‐coding strands with the two‐sets of transcripts derived from adjacent but essentially non‐overlapping regions located greater than 1 kb from the translocation junction. In X63Ag8, where c‐myc is translocated to the immunoglobulin C gamma 2b gene, the c‐myc non‐coding strand transcripts include the translocation junction and then splice directly into the gamma 2b CH1 exon. We propose that chromosome translocation activates a cryptic promoter in the first intron and that the heterogeneously initiated, bipolar transcription reflects the absence of a suitably placed TATA box element.