Genetic suppression analysis of non-antibiotic-producing mutants of the Streptomyces coelicolor absA locus

The absA locus in Streptomyces coelicolor A3(2) was identified because muta tions in it uncoupled sporulation from antibiotic synthesis: absA mutants f ailed to produce any of the four antibiotics characteristic of S. coelicolo r. These mutants are now shown to contain point mutations in the aksA1 gene which encodes the histidine kinase sensor-transmitter protein of a two-com ponent signalling system. The absA1 non-antibiotic-producing mutants, which are unpigmented, spontaneously acquire pigmented colony sectors. Genetic a nalysis established that the pigmented sectors contain second-site suppress ive mutations, sab (for suppressor of abs). Phenotypic characterization sho wed that sab strains produce all four antibiotics; some overproduce antibio tics and are designated Pha, for precocious hyperproduction of antibiotics. A set of sab mutations responsible for suppression was localized by plasmi d-mediated and protoplast fusion mapping techniques to the vicinity of the absA locus. DNA cloned from this region was used to construct phage that co uld transduce sab mutations. Sequence analysis of sab strains defined sab m utations in both the absA1 gene and the absA2 gene; the latter encodes the two-component system's response regulator.