Additional copies of the actII regulatory gene induce actinorhodin production in pleiotropic bld mutants of Streptomyces coelicolor A3(2)

Summary: In S. coelicolor there are mutants (named bld) which fail to form aerial mycelium and which are also pleiotropically blocked for synthesis of several antibiotics, including the blue compound actinorhodin. Using a high copy-number vector, a DNA fragment was cloned which restored actinorhodin production, but not aerial mycelium formation, to bldA, D, F, G and H mutants. Subcloning and Southern blotting revealed that the fragment was from the region (actII) that regulates actinorhodin biosynthesis. The ability to elicit actinorhodin production and to complement an actII mutant was localized to a 1·3 kb fragment. These results indicate that the structural genes for actinorhodin biosynthetic enzymes do not contain targets for the bldA, D, F, G and H gene products, and suggest that the corresponding bld genes control actinorhodin synthesis principally via a single gene in the actII regulatory region.