Morphogenetic Signaling Molecules of the Streptomycetes

The streptomycetes are soil dwelling Gram-positive bacteria that have evolved metabolic and morphological adaptations to enable their success in this harsh environment. While the extracellular stimulation of both streptomycin production and morphological differentiation by A-factor in S. griseus had been well established, the importance of extracellular communication in S. coelicolor did not become apparent until the early 1990s. The general mechanism by which GBLs exert their cellular effects is conserved as they typically bind to intracellular receptors that function as repressors. In this way, GBL-receptor interaction modulates the expression of target genes. Early attempts to develop a S. griseus streptomycin production strain were hindered by unstable A-factor biosynthesis. The A-factor receptor, ArpA, belongs to the TetR family of transcriptional repressors, and as such consists of a regulatory, ligand-binding domain and a helix-turn-helix domain that binds palindromic sequences within the target DNA.