THE 5'-UNTRANSLATED REGION OF THE IGF-I RECEPTOR GENE MODULATES REPORTER GENE-EXPRESSION BY BOTH PRETRANSCRIPTIONAL AND POSTTRANSCRIPTIONALMECHANISMS

The insulin-like growth factor I(IGF-I) receptor gene has a large, com plex 5'-untranslated region (UTR). In order to examine the role that t his region plays in regulating IGF-I receptor expression, we isolated fragments of the human IGF-I receptor 5'-UTR and interposed them betwe en the SV40 early promoter and the chloramphenicol acetyl transferase reporter gene. Fragments of the IGF-I receptor gene 5'-UTR were found to enhance reporter gene expression by increasing gene transcription. In addition, the increased transcription and mRNA levels were in exces s of the increase in enzyme activity, providing indirect evidence that these fragments inhibit translation, consistent with predictions.