AUUUA motifs are dispensable for rapid degradation of the mouse c-myc RNA.

Sequence determinants responsible for c-myc RNA rapid turn-over are localized within the 3' non-coding region which is mainly characterized by the presence of two polyadenylation signals and a high content in A and U. Although the AUUUA/UUAUUUA motif is commonly thought to specify a whole class of unstable RNAs coding for various onco-proteins and cytokines, site-directed mutagenesis showed that both of the two such sequences found in the mouse c-myc RNA are dispensable for rapid RNA degradation. Although less efficient than the whole 3' non-coding region, the last 50 nucleotides of c-myc RNA, mainly made up of U and A and devoid of AUUUA/UUAUUUA motif, are sufficient to confer instability to the coding sequence.