The two branched-chain ?-keto acid dehydrogenase complexes of streptomyces coelicolor differentially regulate morphogenesis and antibiotic production
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The primary objective of this work was to determine the role of the two branched-chain±-keto acid dehydrogenases (BCDH) of Streptomyces coelicolor in morphogenesis and antibioticproduction. Deletion mutants of the two clusters have been constructed and analysis of themutants has led to the determination that bkdA1B1C1 encodes the BCDH complex responsiblefor utilizing the branched-chain amino acids as sole carbon sources, for initiating morphogenesis,and for producing precursors for branched-chain fatty acid production and for actinorhodinproduction. A deletion mutant of the bkdA2B2C2 cluster was unable to be constructed without asecond copy under the control of an inducible promoter present, suggesting that bkdA2B2C2 isessential for viability. The bkdA2B2C2 cluster also encodes the BCDH complex responsible forproviding the precursors for ³-butyrolactone production, and for initiating morphogenesis. Thefact that deletion of each cluster has a phenotype in the presence of a wild-type copy of the othercluster suggests that the temporal expression differences, the potential of the BCDH enzymesforming multi-enzyme complexes, or the possibility that some of the substrates of the reactionsthey catalyze may not be freely exchangeable may play major roles in the differential functionsof the two clusters.Characterization of a new IS-like element from the Streptomyces temperate bacteriophageÆMrT will also be presented. The IS-like element is capable of transposition in several speciesof Streptomyces, and may be responsible for integration of ÆMrT into the Streptomyceschromosome. Because the IS-like element is active in many species of Streptomyces, it may beuseful for designing of stably integrating vectors to engineer industrially important strains ofstreptomycetes that produce important antimicrobial compounds.