1995 Volume 9 Issue 2 Pages 244-253
The genus Streptomyces is characterized by its ability to produce a wide variety of secondary metabolites and complex morphological differentiation resembling that of fungi. The regulation controlling these two characteristic aspects include “eucaryotic” systems, such as a hormonal control represented by the A-factor regulatory system and protein phosphorylation represented by the afsK/afsR system. A-factor is a chemical signaling molecule that triggers both secondary metabolite formation and aerial mycelium formation in Streptomyces griseus. Characterization of the A-factor-specific receptor gene suggests that the receptor acts as a repressor-type regulator for secondary metabolite formation and morphogenesis during the early stage of growth and A-factor at a certain critical intracellular concentration releases the derepression, thus leading to the onset of secondary metabolism and aerial mycelium formation. The A-factor signal is then transferred, via one or more steps, to a transcriptional activator for the strR gene, a transcriptional activator for the whole streptomycin biosynthetic genes. Involvement of protein serine/threonine kinases in signal transduction leading to antibiotic production and morphogenesis, either as a member in the A-factor regulatory cascade or as a regulator in the pathway independent of the cascade, has also been demonstrated by the studies with afsK/afsR of Streptomyces coelicolor A3(2) and their homologs of S. griseus.
