ROLE OF THE 3'-UNTRANSLATED REGION OF RPE65 MESSENGER-RNA IN THE TRANSLATIONAL REGULATION OF THE RPE65 GENE - IDENTIFICATION OF A SPECIFIC TRANSLATION INHIBITORY ELEMENT

Previously, we demonstrated that explanted bovine retinal pigment epit helium (RPE) cells lose RPE65 protein, a major microsomal protein spec ific to RPE, while the RPE65 mRNA remains, suggesting posttranscriptio nal regulation of RPE65 expression in vitro. Accordingly, we analyze h ere the effect of the 5'- and 3'-untranslated regions (UTRs) of RPE65 mRNA on translational efficiency using in vitro translation systems. W e 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 inhi bitory element (TIE) is contained within the 170-nucleotide (nt) seque nce downstream of the stop codon, There is also a weak destabilizing e ffect that is associated with the region 3' to the putative TIE. But t he effect of this is much less than that of the TIE. This TIE, however , does not inhibit translation of the heterologous chloramphenicol ace tyltransferase gene, suggesting that a specific interaction with the u pstream RPE65 coding sequence, or its product, may be required. Thus, the posttranscriptional regulation of RPE65 mRNA expression observed i n cultured RPE may be via a mechanism of translational inhibition.