THE PPGPP SYNTHETASE GENE (RELA) OF STREPTOMYCES-COELICOLOR A3(2) PLAYS A CONDITIONAL ROLE IN ANTIBIOTIC PRODUCTION AND MORPHOLOGICAL-DIFFERENTIATION

Deletion of most of the coding region of the ppGpp synthetase gene (re lA) of Streptomyces coelicolor A3(2) resulted in loss of ppGpp synthes is, both upon entry into stationary phase under conditions of nitrogen limitation and following amino acid starvation during exponential gro wth, but had no effect on growth rate, The relA mutant, which showed c ontinued rRNA synthesis upon amino acid depletion (the relaxed respons e), failed to produce the antibiotics undecylprodigiosin (Red) and act inorhodin (Act) under conditions of nitrogen limitation, The latter ap pears to reflect diminished transcription of pathway-specific regulato ry genes for Red and Act production, redo and actII-ORF4, respectively , In addition to the changes in secondary metabolism, the relA mutant showed a marked delay in the onset and extent of morphological differe ntiation, resulting in a conspicuously altered colony morphology.