Signal transduction and secondary metabolism: prospects for controlling productivity.

Evidence is accumulating that demonstrates the key roles played by diffusible molecules in regulating cellular differentiation, even among prokaryotic microorganisms. This is exemplified by A-factor and its analogues, which act as autoregulators for morphological differentiation and secondary metabolism in Streptomyces. The identification of a specific receptor for A-factor and an A-factor-controlled promoter sequence in S. griseus indicate the close similarity of this system to eukaryotic hormonal control. The involvement of prokaryotic homologues of the eukaryotic Ser/Thr-kinases in the regulation of differentiation processes seems to be another characteristic feature of this group of bacteria. Recent evidence for the presence of these molecular signalling systems in Streptomyces is reviewed, along with the inherent implications.