A COMMON ANCESTOR FOR HUMAN PLACENTAL 17-BETA-HYDROXYSTEROID DEHYDROGENASE, STREPTOMYCES-COELICOLOR ACTIII PROTEIN, AND DROSOPHILA-MELANOGASTER ALCOHOL-DEHYDROGENASE

A computer-based comparison of the amino acid sequences of human placental 17β-hydroxysteroid dehydrogenase and Streptomyces coelicolor actIII protein, which is important in the synthesis of the antibiotic actinorhodin, gives an alignment score 12.15 standard deviations higher than that of 1000 comparisons of randomized sequences of these proteins. The probability of getting this score by chance is 3 x 10-34. Comparison of actIII protein with Drosophila melanogaster alcohol dehydrogenase yields a score of 10.3 standard deviations (P = 3.5 x 10-25). Based on these similarities, we propose that 17β-dehydroxysteroid dehydrogenase, actIII protein, and Drosophila alcohol dehydrogenase are derived from a common ancestor.