Abstract
The enzyme 3β-hydroxysteroid dehydrogenazse (3βHSD) is essential for all steroid hormone biosynthesis. Six distinct 3βHSD cDNAs in the mouse (3βHSD I–VI) have been isolated previously. This study reports the isolation of genes or partial genes encoding the 3βHSD I, II, III, and IV isoforms. Characterization of the genes revealed that they consist of four exons, the same structure that has been observed for characterized human 3βHSD genes. Primer extension and nuclease S1 analysis identified the start sites of transcription of Hsd3b-1 and -4. The proximal promoter regions of Hsd3b-1 and -4 were sequenced and putative cis-acting sequences were determined. Previously, we reported that the then known 3βHSD genes (3βHSD I–IV) were located in a small region of mouse chromosome 3. To analyze this locus further, six yeast artificial chromosome clones containing the 3βHSD sequence were identified. One clone appears to contain the complete 3βHSD locus within its 1,400-kbp insert. Further analysis of this YAC, along with analysis of mouse genomic DNA by pulsed-field gel electrophoresis, suggests all members of the 3βHSD gene family may be contained on a 400-kbp fragment.
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