Insertional inactivation of mtrX and mtrY genes from the mithramycin gene cluster affects production and growth of the producer organism Streptomycesargillaceus

Mithramycin is an antitumor aromatic polyketide synthesized by Streptomyces argillaceus. Two genes (mtrX and mtrY) of the mithramycin gene cluster wer e inactivated by gene replacement. Inactivation of mtrX, that encodes an AB C excission nuclease system for DNA repair, produced a mutant that was affe cted in the normal rate of growth. Expression of mtrX in Streptomyces aibus in a multicopy plasmid vector conferred a low increase in resistance to mi thramycin. Inactivation of mtrY, that encodes a protein of unknown function , produced a 50% decrease in mithramycin biosynthesis. When mtrY was expres sed in the wild-type S. argillaceus in a multicopy plasmid, this caused abo ut 47% increase in the levels of mithramycin production. It is proposed tha t mtrX and mtrY could code for a secondary defense mechanism and a mithramy cin regulatory element, respectively. (C) 2000 Federation of European Micro biological Societies. Published by Elsevier Science B.V. All rights reserve d.