Translational regulation of human beta interferon mRNA: Association of the 3′ AU-rich sequence with the poly(A) tail reduces translation efficiency in vitro

The 3′ AU-rich region of human beta-1 interferon (hu-IFNβ) mRNA was found to act as a translational inhibitory element. The translational regulation of this 3′ AU-rich sequence and the effect of its association with the poly(A) tail were studied in cell-free rabbit reticulocyte lysate. A poly(A)-rich hu-IFNβ mRNA (110 A residues) served as an inefficient template for protein synthesis. However, translational efficiency was considerably improved when the poly(A) tract was shortened (11 A residues) or when the 3′ AU-rich sequence was deleted, indicating that interaction between these two regions was responsible for the reduced translation of the poly(A)-rich hu-IFNβ mRNA. Differences in translational efficiency of the various hu-IFNβ mRNAs correlated well with their polysomal distribution. The poly(A)-rich hu-IFNβ mRNA failed to form large polysemes, while its counterpart bearing a short poly(A) tail was recruited more efficiently into large polysemes. The AU-rich sequence-binding activity was reduced when the RNA probe contained both the 3′ AU-rich sequence and long poly(A) tail, supporting a physical association between these two regions. Further evidence for this interaction was achieved by RNase H protection assay. We suggest that the 3′ AU-rich sequence may regulate the translation of hu-IFNβ mRNA by interacting with the poly(A) tail.