Elongation factor 1α binds to the region of the metallothionein-1 mRNA implicated in perinuclear localization—importance of an internal stem–loop

摘要

In eukaryotic cells, mRNA localization can provide local protein synthesis. Metallothionein-1 (MT-1) mRNA is associated with the perinuclear cytoskeleton, and this is essential for subsequent nuclear import of the protein. The present study defines the cis-acting localization signal and a trans-acting binding protein. Gel retardation and UV cross-linking assays using MT-1 3′UTR transcripts and CHO cell extracts revealed formation of a complex containing a ∼50-kDa protein. Only localization-positive mutant transcripts competed for binding of this protein. Using an RNA affinity technique, Western blotting, mass spectrometry, and a supershift assay, the protein was identified as Elongation factor 1α (eEF1α). Mutation and deletion analysis showed that two regions, nucleotides 21–36 and 66–76, were required for both binding and localization. RNA-folding prediction combined with chemical and enzymatic probing experiments suggest that these regions are in juxtaposition within a stem/internal loop structure. Mutations that are predicted to alter this structure abrogate protein binding. Our hypothesis is that the cis-acting signal in MT-1 3′UTR is formed by this stem/internal loop, that it binds eEF1α, and that eEF1α–cytoskeleton interactions play a role in perinuclear mRNA localization.