DETERMINANTS OF DROSOPHILA-FUSHI-TARAZU MESSENGER-RNA INSTABILITY

The fushi tarazu gene is essential for the establishment of the Drosop hila embryonic body plan. When first expressed, in early embryogenesis , fushi tarazu mRNA is uniformly distributed over most of the embryo. Subsequently, fushi tarazu mRNA expression rapidly evolves into a patt ern of seven stripes that encircle the embryo. The instability of fush i tarazu mRNA is probably crucial for attaining this localized pattern of expression. mRNA stability in transgenic embryos was measured by a new method that does not use drugs or external interference. Experime nts using hybrid genes that fuse fushi tarazu sequences to those of th e stable ribosomal protein Al mRNA provide evidence for at least two d estabilizing elements in the fushi tarazu mRNA, one located within the 5' one-third of the mRNA and the other near the 3' end (termed FIE3 f or ftz instability element 3'). The FIE3 lies within a 201-nucleotide sequence just upstream of the polyadenylation signal and can act auton omously to destabilize a heterologous mRNA. Further deletion construct s identified an essential 68-nucleotide element within the FIE3. Lack of homology between this element and other previously identified desta bilization sequences suggests that FIE3 contains a novel RNA destabili zation element.