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Summary

In Streptomyces griseus, A-factor (2-isocapryloyl-3R-hydroxymethyl-γ-butyrolactone) triggers morphological development and secondary metabolism by inducing a pleiotropic transcriptional regulator AdpA. Extracellular proteome analysis of the wild-type and ΔadpA strains grown to the end of the exponential phase in liquid minimal medium revealed that 38 secreted proteins, including many catabolic enzymes, such as protease, glycosyl hydrolase and esterase, were produced in an AdpA-dependent manner. Transcriptome analysis showed that almost all of these AdpA-dependent secreted proteins were regulated at the transcriptional level. In vitro AdpA-binding assays and determination of transcriptional start sites led to identification of 11 promoters as novel targets of AdpA. Viability staining revealed that some hyphae lysed during the exponential growth phase, which could explain the detection of 3 and 23 cytoplasmic proteins in the culture media of the wild-type and ΔadpA strains respectively. In the wild-type strain, due to high protease activity in the culture medium, cytoplasmic proteins that leaked from dead cells seemed to be degraded and reused for the further growth. The existence of many AdpA-dependent (i.e. A-factor-inducible) secreted catabolic enzymes, which are likely involved in the assimilation of material that leaked from dead cells, reemphasizes the importance of A-factor in the morphological differentiation of S. griseus.