Implication of a repression system, homologous to those of other bacteria, in the control of arginine biosynthesis genes in Streptomyces coelicolor.

As with most amino acid biosynthetic pathways in streptomycetes, enzymes of arginine biosynthesis in Streptomyces coelicolor show only slight derepression in minimal medium without, as opposed to with, exogenous arginine. However, when an arginine auxotroph was cultured in limiting arginine, ornithine carbamoyltransferase (OCT) activities rose by as much as 100-fold. The response was not due to a general starvation effect. To elucidate the repression-derepression mechanism, a DNA fragment containing the upstream region of the previously isolated S. coelicolor argCJB cluster was cloned into a multicopy vector and transformed into wild-type S. coelicolor; a slight transient derepression of OCT was observed in minimal medium without, though not with, added arginine, consistent with titration by the insert of a negatively acting macromolecule such as a repressor. A subfragment carrying the 5' end of argC and the region immediately upstream showed specific binding, in mobility shift assays, to purified AhrC, the repressor/activator of genes of arginine metabolism in Bacillus subtilis. It is therefore likely that in S. coelicolor, expression of arginine biosynthesis genes is controlled by a protein homologous to the well-characterised B. subtilis and Escherichia coli repressors.