Background/Aims: A-factor, a γ-butyrolactone autoregulator, in Streptomyces griseus is involved in the regulation of differentiation and antibiotic production. Here we studied the S. griseus B2682-AFN (A-factor negative) bald mutant that harbors a nonsense mutation in the afsR gene encoding a pleiotropic regulator. Our aim was to prove that this mutation is the cause of the A-factor deficiency in AFN. We also studied whether AfsR regulates A-factor production by AfsA, which is supposed to be the only specific key enzyme in A-factor biosynthesis. Methods: Wild afsR was cloned to the pHJL401 shuttle vector and was transformed to the S. griseus AFN and B2682 strains. During phenotypic characterization, sporulation, antibiotic, protease, A-factor, and AfsA protein production were studied. Results: Transformation of AFN by a wild afsR restored its phenotype including sporulation, antibiotic, extracellular protease, and A-factor production. Introduction of afsR to the B2682 wild-type strain resulted in antibiotic and extracellular protease overproduction that was accompanied with an elevated A-factor level. AfsA was detected both in AFN and B2682. Conclusions: AfsR has an effect on the regulation of A-factor production in S. griseus. The presence of AfsA is not sufficient for normal A-factor production. AfsR regulates A-factor biosynthesis independently of AfsA.

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