GENE STRUCTURE OF BOVINE ADRENODOXIN REDUCTASE

The gene structure of bovine adrenodoxin reductase, a component of the mitochondrial steroid hydroxylating system in the adrenal cortex, was determined. When we screened a bovine genomic DNA library, using bovi ne adrenodoxin reductase cDNA as a probe, we isolated 10 genomic clone s covering a continuous 30 kilobase (kb) region of bovine chromosomal DNA in which the adrenodoxin reductase gene spanned approximately 12 k b. The adrenodoxin reductase gene consisted of 12 exons and all the do nor and acceptor sites of the exon/intron junction followed the GT/AG rule. The transcription initiation site was found to be 79 bases upstr eam of the translation initiation site by primer extension analysis an d putative CAAT and GC boxes, but no typical TATA box, were present in the 5'-flanking region. The 5'-flanking region of this gene showed se veral features characteristic of promoters of house-keeping genes. The CCAGGG sequence present in the 5'-flanking region of genes for adreno doxin and the steroid hydroxylating cytochromes P-450 in the adrenal c ortex was present 13 bases upstream from the transcription initiation site. We analyzed the promoter activity of the 5'-upstream region of t his gene, using as a reporter the chloramphenicol acetyltransferase ge ne. The region between position -757 to -376 was proved necessary for expression of this gene in mouse Y-1 tumor cells. Adrenocorticotropin did not enhance the expression of this bovine gene in the cells.