Role of the 3'-untranslated region of RPE65 mRNA in the translational regulation of the RPE65 gene: identification of a specific translation inhibitory element.

Previously, we demonstrated that explanted bovine retinal pigment epithelium (RPE) cells lose RPE65 protein, a major microsomal protein specific to RPE, while the RPE65 mRNA remains, suggesting posttranscriptional regulation of RPE65 expression in vitro. Accordingly, we analyze here the effect of the 5'- and 3'-untranslated regions (UTRs) of RPE65 mRNA on translational efficiency using in vitro translation systems. We compared the levels of translation products and mRNA stability among RPE65 transcripts containing deletions of the 5'- and 3'-UTRs. First, the 5'-UTR does not affect translational efficiency. However, the 3'-UTR does influence translation efficiency. A putative translation inhibitory element (TIE) is contained within the 170-nucleotide (nt) sequence downstream of the stop codon. There is also a weak destabilizing effect that is associated with the region 3' to the putative TIE. But the effect of this is much less than that of the TIE. This TIE, however, does not inhibit translation of the heterologous chloramphenicol acetyltransferase gene, suggesting that a specific interaction with the upstream RPE65 coding sequence, or its product, may be required. Thus, the posttranscriptional regulation of RPE65 mRNA expression observed in cultured RPE may be via a mechanism of translational inhibition.