The endonuclease activity of RNase III is required for the regulation of antibiotic production by Streptomyces coelicolor

The double strand-specific endoRNase RNase III globally regulates the production of antibiotics by Streptomyces coelicolor. We have undertaken studies to determine whether the endoRNase activity of S. coelicolor RNase III or its RNA binding activity is responsible for its regulatory function. We show that an rnc null mutant of S. coelicolor M145 does not produce actinorhodin or undecylprodigiosin. Restoring a wild-type copy of rnc to that mutant also restored antibiotic production. We constructed an rnc point mutant, D70A, in which an aspartic acid residue which is essential for the catalytic activity of RNase III was changed to alanine. The D70A mutation abolished the catalytic activity of the protein but not its ability to bind to RNA substrates. Introduction of a copy of the D70A gene into the rnc null mutant did not restore antibiotic production. This result suggests that the endoRNase activity of RNase III is required for the regulation of antibiotic production in S. coelicolor. We also reconstructed the C120 point mutation that was originally described in 1992. Although that mutation diminished antibiotic production by S. coelicolor, we confirm here that the C120 protein retains some RNase III activity.