Identification of an activity that interacts with the 3'-untranslated region of c-myc mRNA and the role of its target sequence in mediating rapid mRNA degradation.

Single or multiple copies of the pentameric motif, AUUUA, are found in the 3'-untranslated domain of most immediate early mRNAs. A broad body of data links this 5-base element to the selective degradation of these mRNAs. However, AUUUA motifs are neither always necessary nor always sufficient to tag an mRNA for rapid degradation. Here, we describe a cytoplasmic, protease-sensitive factor in Balb/c3T3 cells that interacts with the 3'-untranslated region of c-myc mRNA. The factor recognizes a 39-base uridine-rich domain adjacent to, but distinct from, the c-myc AUUUA motif. In chimeric mRNA constructs, the 39-base binding element cooperates with adjacent sequence material to destabilize beta-globin mRNA.