Role of RNA structures m c- myc and c- fos gene regulations

Proto-oncogenes c- myc and c- fos are subjected to a complex set of controls operating both at the transcriptional and post-transcriptional levels. We report here that: (i) antisense transcription occurs at the murine c- myc locus. However, its biological significance remains to be established; (ii) transcription of both genes is regulated in various situations by a block to elongation of nascent RNA chains. In the case of c- myc, the blockade involves a RNA structure whose nature remains unknown; (iii) elements responsible for the high degree of instability of c- myc and c- fos mRNAs reside in their 3' non-coding regions. A U-rich region, reminiscent of that present in the granulocyte-monocyte colony-stimulating factor mRNA destabilizer, is likely to be involved in the rapid degradation of c- fos mRNA; (iv) exon 1 substitution by intron 1-derived sequences lessens or negates the effect of the 3' destabilizer in abnormal c- myc RNAs from Burkitt's lymphomas and mouse plasmacytomas.