Abstract 16

The duplicated C4/21OH region is a complex gene locus and in which 13 different transcripts are encoded within 75-80 kb. Nine of these transcripts are expressed in adrenal cortex, suggesting the presence of a single locus control region. The Z gene was identified as a unique 1 kb RNA TRANSCRIPT, that arises from a cryptic promoter lying in the intron between exons 35 and 36 of C4 gene (Hum Ml Genet 4:2109, 1995). The aim of this study was to determine if the Z promoter contributes to CYP21B gene expression. We built promoter/reporter constructions containing 5.8, 4.8, 4.0, 3.5, 1.6 or 0.3 kb of the 5'flanking DNA upstream from the human CYP21B gene, linked to the luciferase reporter gene and we measured luciferase activity in transfected Y-1 cells. Basal activity was determined in the presence of 0.3 kb construction, which included CYP21B promoter. A significant increment in the luciferase activity was observed only in cells transfected with constructions containing 5.8 kb upstream from the CYP21B gene (n=4, p=0.027). These data identify the presence of a positive regulatory element between 4.8 and 5.8 kb upstream from CYP21B gene. As this region contains the entire promoter of the Z gene, the Z promoter might be involved in the CYP21B expression.