THE AERIAL MYCELIUM-DEFECTIVE PHENOTYPE OF STREPTOMYCES-GRISEUS RESULTING FROM A-FACTOR DEFICIENCY IS SUPPRESSED BY A SER THR KINASE OF S-COELICOLOR A3(2)/

A-factor isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone) is essenti al for aerial mycelium formation and streptomycin (Sm) production in S treptomyces griseus, A protein Ser/Thr kinase (AfsK), the product of t he Streptomyces coelicolor A3(2) afsK gene, controlling secondary meta bolism in this strain, reversed the aerial mycelium-negative phenotype of an A-factor-deficient mutant strain, S. griseus HH1, and induced s porulation without affecting A-factor productivity or Sm production. A mutant AfsK protein lacking kinase activity failed to induce aerial m ycelium formation which indicates the importance of the kinase activit y for suppression in S. griseus. These data suggest that a Ser/Thr kin ase functionally similar to S. coelicolor A3(2) AfsK plays a regulator y role in aerial mycelium formation in S. griseus, either as a member in the A-factor regulatory network or independently of this network.