Functional Mapping of Destabilizing Elements in the Protein-coding Region of the Drosophila fushi tarazu mRNA

The instability of the fushi tarazu (ftz) mRNA is essential for the proper development of the Drosophila embryo. Previously, we identified a 201-nucleotide instability element (FIE3) in the 3′ untranslated region (UTR) of the ftz mRNA. Here we report on the identification of two additional elements in the protein-coding region of the message: the 63-nucleotide-long FIE5-1 and the 69-nucleotide-long FIE5-2. The function of both elements was position-dependent; the same elements destabilized RNAs when present within the coding region but did not when embedded in the 3′ UTR of the hybrid mRNAs. We conclude that ftz mRNA has three redundant instability elements, two in the protein-coding region and one in the 3′ UTR. Although each instability element is sufficient to destabilize a heterologous mRNA, the destabilizing activity of the two 5′-elements depended on their position within the message.