Functional localization signals extend throughout the length of An1 mRNA. (A) Scheme showing the location of E2 and VM1 motifs in the An1 3′ UTR targeted for mutagenesis (left). Empty symbols represent sites of mutation. Localization phenotypes of injected RNAs (right). Following immunohistochemical staining of oocytes injected with DIG-labeled RNA, each was visually judged for localization. Representative oocytes injected with each RNA are shown along the side of the table oriented with the animal hemisphere upward. (B) UV cross-linking and localization assays of Vg1 and An1 mRNAs. Full-length Vg1 mRNA (lane 1) is cross-linked to the six core group of proteins. Deletion of the Vg1 3′ UTR, which removes the VLE, eliminates cross-linking of the binding proteins (lane 2) and abolishes localization of the RNA. Deletion of the An1 3′ UTR (lane 3) or the 3′ UTR and the last 850 nt of the ORF (lane 4) do not eliminate cross-linking activity or localization of these mutant RNAs.
