Alternate structures and stabilities of c-myc RNA in a bursal lymphoma cell line.

A bursal lymphoma cell line, BK25, had been shown to be haploid at the c-myc locus and to have undergone an alteration of chromatin structure upstream from the c-myc coding region. In BK25 DNA at least the 3' half of an ALV provirus is integrated 160bp upstream from exon 2. As a result of this integration event, the first and second exons are separated by at least 17 kb. Approximately 90% of c-myc transcription begins in the promoter of the ALV proviral long terminal repeat (LTR) and this mRNA has a half-life of approximately 25 minutes in actinomycin D chase experiments. Approximately 10% of c-myc transcription initiates at the normal promoter of c-myc. The latter message has an unusually long half-life of greater than 100 minutes. By contrast, in MSB-1 cells, which lack any c-myc rearrangements, transcription begins at the normal promoter in exon 1 and c-myc RNA has a half-life of approximately 15 minutes. These results suggest that factors in addition to the structure of the 5' end of chicken c-myc RNA determine its stability in vivo.