We are investigating a developmental switch in hormonal regulation ofβ1AR gene expression. The lack of hormone responsiveness of the β1AR in the fetus and upregulation by steroids and thyroid hormones in the newborn and adults may represent a unique transcription mechanism of this physiologically critical receptor. To study this, we have cloned the ovineβ1AR gene and 2.3 kb of promoter sequence. Transient expression studies indicated that deletion of sequences between 1530 and 953 markedly increased transcription activity and may contain a repressor element. This region also encompasses a putative glucocorticoid response element (GRE1) and an AP1 site. A 186bp PCR fragment containing GRE1 was subcloned into a reporter vector. Dexamethasone, when cotransfected with the GRE1 and a vector expressing the glucocorticoid receptor, increased the transcription activity significantly in SKNMC but not in C6 cells. Gel retardation assay using the GRE1 DNA fragment also confirmed this cell type specific effect. Band shifts were observed in SKNMC but not in C6 cell nuclear extracts. DNase I footprinting assay also identified 3 sites resistant to DNase I. We conclude 1) GRE1 confers glucocorticoid response, an effect that is celltype specific and requires the presence of glucocorticoid receptor. 2) Glucocorticoid responsiveness is colocalized to a region which represses transcription. We speculate that mechanisms operating within this region in the ovine β1AR promoter may be responsible for its unique transcription regulation.