<jats:title>ABSTRACT</jats:title> <jats:p> A mutation in <jats:italic>act</jats:italic> VI-ORF1, which controls C-3 reduction in actinorhodin biosynthesis by <jats:italic>Streptomyces coelicolor</jats:italic> , was complemented by <jats:italic>gra</jats:italic> -ORF5 and -ORF6 from the granaticin biosynthetic gene cluster of <jats:italic>Streptomyces violaceoruber</jats:italic> Tü22. It is hypothesized that, while <jats:italic>gra</jats:italic> -ORF5 alone is a ketoreductase for C-9, <jats:italic>gra</jats:italic> -ORF6 gives the enzyme regiospecificity also for C-3.