CLONING OF THE PROMOTER-REGULATORY REGION OF THE MURINE GROWTH-HORMONE RECEPTOR GENE - IDENTIFICATION OF A DEVELOPMENTALLY-REGULATED ENHANCER ELEMENT

The growth hormone (GH) receptor is essential for the actions of GH on postnatal growth and metabolism. To identify DNA sequences involved i n the regulation of transcription of the murine GH receptor gene, a 17 -kilobase genomic clone containing the 5'-flanking region, exon 1, and part of intron 1 of the murine GH receptor gene was isolated. Utilizi ng primer extension and ribonuclease protection assays, two major tran scription start sites were identified in RNA from liver of male, femal e, and pregnant mice. Transient transfection stud ies using a reporter gene demonstrated promoter activity in a variety of eukaryotic cells. Deletional analysis and DNA protein binding assays led to the identif ication of a 30-base pair enhancer element located about 3.4 kilobases upstream of the transcription start sites. Computer analysis of the n ucleotide sequence of the enhancer element did not reveal any potentia l DNA binding motifs for known transcription factors, and this DNA ele ment failed to exhibit binding activity for some common transcription factors. Analysis of both functional activity and DNA-protein binding activity of this enhancer element in adult and fetal hepatocytes sugge sts that this DNA element may play a role in the developmental express ion of the GH receptor gene.