A single amino acid substitution in region 1.2 of the principal a factor of Streptomyces coelicolor A3(2) results in pleiotropic loss of antibiotic production

Antibiotic production in streptomycetes generally occurs in a growth phase- dependent and developmentally co-ordinated manner, and is subject to pathwa y-specific and pleiotropic control, Streptomyces coelicolor A3(2) produces at least four chemically distinct antibiotics, including actinorhodin (Act) and undecylprodigiosin (Red). afsB mutants of S. coelicolor are deficient in the production of both compounds and in the synthesis of a diffusible ga mma-butyrolactone, SCB1, that can elicit precocious Act and Red production. Clones encoding the principal and essential a factor (sigma(HrdB)) Of S. c oelicolor restored Act and Red production in the afsB mutant BH5. A highly conserved glycine (G) at position 243 of sigma(HrdB) was shown to be replac ed by aspartate (D) in BH5. Replacement of G243 by D in the afsB(+) strain M145 reproduced the afsB phenotype. The antibiotic deficiency correlated wi th reduced transcription of acfII-ORF4 and redo, pathway-specific regulator y genes for Act and Red production respectively. Exogenous addition of SCB1 to the G-243D mutants failed to restore Act and Red synthesis, indicating that loss of antibiotic production was not a result of the deficiency in SC B1 synthesis. The G-243D substitution, which lies in the highly conserved 1 .2 region of undefined function, had no effect on growth rate or morphologi cal differentiation, and appears specifically to affect antibiotic producti on.