LAUSR

Actinomycin peptide synthetase genes constitute two oppositely oriented transcriptional units, acmADR, and acmBC, separated by a non‐coding intergenic region. Gene constructs of the intergenic region together with its adjoining gene acmA or acmB from the actinomycin biosynthetic gene cluster of Streptomyces chrysomallus were transferred into Streptomyces lividans TK64. Each construct expressed the respective synthetase indicating divergent promoters. Primer extension revealed for both directions −10 and −35 boxes similar to σ70‐dependent promoters from Streptomyces and E. coli. No conspicuous regulatory sequences were detected. Accordingly, S. chrysomallus—grown in glucose‐containing medium—produced the peptide synthetases AcmA and AcmB/C as well as actinomycin during logarithmic growth phase. Alignments with the corresponding intergenic region of the actinomycin biosynthetic gene cluster in Streptomyces antibioticus identified analogous −10 and −35 boxes of σ70 consensus sequence. However, in S. antibioticus—cultivated in the same conditions—AcmA and AcmB/C were at maximum activity in late log phase and actinomycin formation peaked in stationary phase. The different patterns of formation of actinomycin and its peptide synthetases encoded by the highly homologous actinomycin biosynthetic gene clusters in S. chrysomallus and S. antibioticus suggest strain‐specific control of biosynthesis in agreement with absence of pathway‐specific regulatory genes.