EXPANSION OF THE MAMMALIAN 3-BETA-HYDROXYSTEROID DEHYDROGENASE PLANT DIHYDROFLAVONOL REDUCTASE SUPERFAMILY TO INCLUDE A BACTERIAL CHOLESTEROL DEHYDROGENASE, A BACTERIAL UDP-GALACTOSE-4-EPIMERASE, AND OPEN READING FRAMES IN VACCINIA VIRUS AND FISH LYMPHOCYSTIS DISEASE VIRUS

Mammalian 3-beta-hydroxysteroid dehydrogenase and plant dihydroflavonol reductases are descended from a common ancestor. Here we present evidence that Nocardia cholesterol dehydrogenase, E coli UDP-galactose-4 epimerase, and open reading frames in vaccinia virus and fish lymphocystis disease virus are homologous to 3-beta-hydroxysteroid dehydrogenase and dihydroflavonol reductase. Analysis of a multiple alignment of these sequences indicates that viral ORFs are most closely related to the mammalian 3-beta-hydroxysteroid dehvdrogenases. The ancestral protein of this superfamily is likely to be one that metabolized sugar nucleotides. The sequence similarity between 3-beta-hydroxysteroid dehydrogenase and the viral ORFs is sufficient to suggest that these ORFs have an activity that is similar to 3-beta-hydroxysteroid dehydrogenase or cholesterol dehydrogenase. although the putative substrates are not vet known.