The block of elongation in c-myc exon 1 is abolished in Burkitt's lymphoma cell lines with variant translocation.

Dimethylsulfoxide (DMSO) induces a block of c-myc RNA elongation in the human B cell line BJAB. In Burkitt's lymphoma cell lines with variant translocations, which are characterized by mutations in and around the first c-myc exon, DMSO is not capable of inducing the RNA elongation block. The action of DMSO is, however, not restricted to regulation at the level of RNA elongation. In the cell line BL2 with a t(8;22) translocation c-myc steady-state RNA decreased about 20 fold 1 and 2 h after DMSO treatment, followed by an increase to approximately initial levels after 4 h. During the time course of the experiment the usage of the dual promoter P1/P2 shifted from the ratio 3:1 in untreated cells to the ratio of 1:5 in BL2 cells treated with DMSO for 4 h. This promoter shift is presumably regulated at the transcriptional level. In BJAB cells an isolated intragenic transcription was detected at the boundary of intron 1 and exon 2. This transcription appeared 2 to 4 h after addition of DMSO when expression of the c-myc gene was downregulated by blocking RNA elongation at the end of exon 1.