The 3' untranslated region of localized maternal messages contains a conserved motif involved in mRNA localization.

Messenger RNA (mRNA) localization is emerging as a means of regulating gene expression. This process is operational in fly and frog development, where a subset of maternally inherited RNAs are asymmetrically distributed and thought to impart axial polarity to the embryo. Since most maternal mRNAs are uniformly distributed, an apparatus must exist to recognize and specifically transport these rare localized species. Here I report the identification of a nine-nucleotide motif, YUGUUYCUG, common to the 3' untranslated regions of four sequenced messages of this class: Drosophila bicoid and nanos mRNAs and Xenopus An2 and Vg1 mRNAs. To test the role of this nonamer sequence in the localization process, a Drosophila transient assay has been established. The assay reveals that bicoid mRNA specifically lacking this nonamer is partially mislocalized. In contrast, nonamer deletion is inconsequential to message stability. The existence of specific and general mRNA localization signals is proposed and it is suggested that this conserved motif belongs to the latter category.