A RESPONSE-REGULATOR-LIKE ACTIVATOR OF ANTIBIOTIC-SYNTHESIS FROM STREPTOMYCES-COELICOLOR A3(2) WITH AN AMINO-TERMINAL DOMAIN THAT LACKS A PHOSPHORYLATION POCKET

In Streptomyces coelicolor A3(2), bldA mutants that lack the tRNA for the rare leucine codon UUA fail to make the red undecylprodigiosin ant ibiotic complex. To find out why, red-pigmented while bald (Pwb) deriv atives of a bldA mutant were isolated. Using a cloning strategy that a llowed for (and demonstrated) dominance of the mutations, they were lo calized to the red gene cluster. By using insert-mediated integration of a phi C31 phage-based vector, one of the Pwb mutations was more pre cisely located between red structural genes to a segment of approximat ely 1 kb about 4 kb from the known pathway-specific regulatory gene re do. The segment contained most of an ORF (redZ) encoding a protein (Re dZ) with end-to-end similarity to response regulators of diverse funct ion from a variety of bacteria. Remarkably, in RedZ hydrophobic residu es replace nearly all of the charged residues that usually make up the phosphorylation pocket present in typical response regulators, includ ing the aspartic acid residue that is normally phosphorylated by a cog nate sensory protein kinase. A single TTA codon in redZ provided a pot ential explanation for the bldA-dependence of undecylprodigiosin synth esis. This codon was unchanged in three Pwb mutants, but further analy sis of one of the mutants revealed a potential up-promoter mutation. I t seems possible that a combination of low-level natural translation o f the UUA codon by a charged non-cognate tRNA, coupled with increased transcription of redZ in the Pwb mutant, allows the accumulation of a threshold level of the Redo protein.