SEQUENCE AND FUNCTIONAL-CHARACTERIZATION OF THE TERMINAL EXON OF THE HUMAN INSULIN-RECEPTOR GENE

We present 5.1 kb of the 3' noncoding region sequence of the human ins ulin receptor gene and identification of four functional polyadenylati on domains responsible for S'-end processing of the 5.4, 6.9, 8.0 and 9.4 kb human insulin receptor mRNA, respectively. The insulin receptor gene contains five putative polyadenylation sites (P1-P5), located 51 60, 6502, 7488, 8945 and 8957 base pairs (bp) downstream from the tran slational initiation site. All putative polyadenylation sites are flan ked by upstream AU rich and downstream GU rich regions which regulate mRNA stability and mRNA cleavage, respectively. Also, two RNA stem-loo p structures have been identified. To determine its role on gene expre ssion, a reporter gene was constructed containing Various lengths of t he insulin receptor 3' UTR and transiently transfected into COS 7 cell s. A 539 bp fragment (4897-5436 bp downstream from the IR translationa l initiation site) inhibited CAT expression by 5-6-fold. Further downs tream addition of 1169 bp of the insulin receptor 3' untranslated regi on enhanced gene expression by 2-fold. These studies provide evidence that the insulin receptor 3' untranslated region can modulate gene exp ression.