IDENTIFICATION OF A LIVER-SPECIFIC PROMOTER FOR THE OVINE GROWTH-HORMONE RECEPTOR

Growth hormone (GH) receptor cDNA clones from several species are char acterized by heterogeneity in the 5' untranslated region (5'UT). This has been attributed to different promoters directing the expression of the gene from exons encoding 5'UT's which are alternatively spliced o nto a common splice acceptor 11 basepairs (bp) upstream of the initiat ing AUG on exon 2. The following study identifies exon 1A of the ovine (o) GH receptor gene, corresponding to the 5'UT of a developmentally regulated, liver-specific transcript. Exon 1A spans 206 bp at a positi on 17 kilobases (kb) upstream of exon 2. Sequencing of the 669 bp regi on 5' to the transcription initiation site (+1) reveals a TATA box at - 31, a CCAAT box at - 88, and putative binding sites for several tran scription factors involved in liver-specific gene expression. Two repe titive sequence elements are located in the 5' and 3' flanking regions of exon 1A. Functional analysis of the 4.5 kb region upstream of exon 1A was performed by transfecting the human hepatoma cell line HuH7 wi th luciferase reporter gene constructs. Positive and negative regulato ry regions are identified, with basal promoter activity within 473 bp of the transcription initiation site. A 47 bp region containing putati ve binding sites for the activated glucocorticoid receptor and C/EBP-l ike proteins, between - 180 and - 133, is essential for transcriptiona l activation.