Human adrenodoxin reductase: Two mRNAs encoded by a single gene on chromosome 17cen→q25 are expressed in steroidogenic tissues

Adrenodoxin reductase is a mitochondrial flavoprotein that receives electrons from NADPH, thus initiating the electron-transport chain serving mitochondrial cytochromes P450. We have cloned and sequenced two human adrenodoxin reductase cDNAs that differ by the presence of six additional codons in the middle of one clone. The sequence in this region indicates that these six extra codons arise by alternative splicing of the pre-mRNA. Southern blot hybridization patterns of human genomic DNA cut with four restriction enzymes indicate that the human genome has only one gene for adrenodoxin reductase. Analysis of a panel of mouse-human somatic cell hybrids localized this gene to chromosome 17cen→q25. The alternatively spliced mRNA containing the six extra codons represents 10-20% of all adrenodoxin reductase mRNA. The expression of the adrenodoxin reductase gene may be stimulated by pituitary tropic hormones acting through cAMP, but its response is quantitatively much less than the responses of P450scc and adrenodoxin.