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Arginine boxes and the argR gene in Streptomyces clavuligerus: evidence for a clear regulation of the arginine pathway

The argR gene of Streptomyces clavuligerus has been located in the upstream region of argG. It encodes a protein of 160 amino acids with a deduced Mr of 17 117 for the monomer. Transformants containing the amplified argR gene showed lower activity (50%) of the biosynthetic ornithine carbamoyltransferase (OTC) activity and higher levels (380%) of the catabolic ornithine aminotransferase (OAT) activity than control strains. Amplification of an arginine (ARG) box‐containing sequence results in a 2‐ to 2.5‐fold derepression of ornithine acetyltransferase and OTC, suggesting that the repressor is titrated out. Footprinting experiments using the pure homologous arginine repressor (AhrC) of B. subtilis showed a protected 38 nt region (ARG box) in the coding strand upstream of argC. The protected region contained two tandemly repeated imperfect palindromic 18‐nt ARG boxes. The repressor–operator interaction was confirmed by band‐shift experiments of the DNA fragment containing the protected region. By computer analysis of the Streptomyces sequences available in the databases, a consensus ARG box has been deduced for the genus Streptomyces. This is the first example of a clear regulation of an amino acid biosynthetic pathway in Streptomyces species, challenging the belief that actinomycetes do not have a well‐developed regulatory system of these pathways.