The 3′ untranslated region of manganese superoxide dismutase RNA contains a translational enhancer element

A redox-sensitive protein that binds to the 3' untranslated region (UTR) of manganese superoxide dismutase (MnSOD) RNA has been described previously [Fazzone, H., Wangner, A., and Clerch, L. B. (1993) J. Clin. Invest. 92, 1278-1281; Chung, D. J., and Clerch, L. B. (1997) Am. J. Physiol. 16, L714-L719]. In the present study, cross-competition gel retardation and RNase H assays were used to identify a 41-base region located 111 bases downstream of the stop codon as the 3' UTR cis element involved in protein binding. The base sequence of this region is similar to 75% conserved among the 3' UTRs of rat, mouse, cow, and human MnSOD mRNAs at approximately the same distance downstream of the stop codon. The role of this protein-binding region in RNA translation was assessed in an in vitro rabbit reticulocyte lysate system. Translation of MnSOD RNA from which the 3' UTR element was deleted decreased 60% compared with translation of MnSOD RNA containing the 3' UTR cis element. In the presence of a specific competitor oligoribonucleotide that inhibits MnSOD RNA protein-binding activity, translation of MnSOD RNA containing the 3' UTR was decreased by 65%. Thus, both the cis element and RNA protein-binding activity were required for more efficient translation of the MnSOD. An analysis of ribosomal profiles suggests the MnSOD RNA-binding protein participates in the formation of the translation initiation complex. When MnSOD RNA-binding activity was inhibited, initiation complex formation was decreased by 50%. From the data obtained in this study, we propose that the 3' UTR cis element of MnSOD through its interaction with MnSOD RNA-binding protein may function as a translational enhancer.