Résumé
c-myc messenger RNAs are known to be extremely unstable (t
1
2
= 10 min) in normal and tumor cells, suggesting that degradation could play an important role in regulating their steady state level in the cytoplasm. We have investigated the stabilities of c-
myc mRNAs in three murine plasmacytomas, where the c-
myc gene either remains intact (ABPC20) or exists in a truncated form (MPC-11 and J558L) subsequent to 6;15 or 12;15 chromosome translocations respectively, and in an A-MuLV-induced pre-B lymphoma line (18–81.5) that lacks chromosome translocations and contains both c-
myc genes in their normal context. The truncated
myc genes in J558L and MPC-11 lack the promoters of the normal gene but are transcribed from cryptic promoters within the first c-
myc intron. We found that posttranscriptional processes are largely responsible for the higher steady state accumulations of truncated c-
myc transcripts, while broken and intact c-
myc genes are transcribed at comparable rates.