AmfS, an Extracellular Peptidic Morphogen in Streptomyces griseus

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Abstract
The amf gene cluster was previously identified as a regulator for the onset of aerial-mycelium formation in Streptomyces griseus . The nucleotide sequences of amf and its counterparts in other species revealed a conserved gene organization consisting of five open reading frames. A nonsense mutation in amfS , encoding a 43-amino-acid peptide, caused significant blocking of aerial-mycelium formation and streptomycin production, suggesting its role as a regulatory molecule. Extracellular-complementation tests for the aerial-mycelium-deficient phenotype of the amfS mutant demonstrated that AmfS was secreted by the wild-type strain. A null mutation in amfBA , encoding HlyB-like membrane translocators, abolished the extracellular AmfS activity without affecting the wild-type morphology, which suggests that AmfBA is involved not in production but in export of AmfS. A synthetic C-terminal octapeptide partially induced aerial-mycelium formation in the amfS mutant, which suggests that an AmfS derivative, but not AmfS itself, serves as an extracellular morphogen.