Aberrant c‐myc RNAs of Burkitt's lymphoma cells have longer half‐lives.

BL67 and BL18 are Burkitt's lymphoma cell lines with t(8;14) translocations (the breakpoint is in the first exon and first intron, respectively) in which the mu‐heavy chain switch region is fused to the c‐myc gene in head to head orientation. In both cell lines only aberrant c‐myc RNAs are found. BL67 cells contain two c‐myc RNA species of 2.4 and 3.5 kb. The 2.4‐kb RNA is initiated at several cryptic promoters in the first intron. The 3.5‐kb RNA is transcribed from the immunoglobulin heavy chain anti‐sense strand across the breakpoint of the translocation into the first exon of the c‐myc gene and is then normally spliced using the physiological splice donor and acceptor sites of the c‐myc gene. BL18 contains c‐myc RNA of 2.4 kb initiated at cryptic promoters in the first intron and additional RNAs of 0.90 kb and 0.74 kb transcribed from the dual c‐myc promoters on the reciprocal fragment of the translocation. The cytoplasmic turnover of these RNAs differs significantly from that of the normal c‐myc message. The 3.5‐kb RNA of BL67 cells and the 0.90‐kb and 0.74‐kb RNAs of BL18 cells, which are both hybrid molecules consisting of c‐myc and immunoglobulin sequences, have a half‐life of several hours in contrast to the normal c‐myc message with a half‐life of 15 min. The aberrant 2.4‐kb c‐myc RNAs of BL67 and BL18 cells are also more stable than the normal c‐myc message and disappear with a half‐life of 50 min.(ABSTRACT TRUNCATED AT 250 WORDS)