AN EXPORTED PEPTIDE FUNCTIONS INTRACELLULARLY TO CONTRIBUTE TO CELL-DENSITY SIGNALING IN BACILLUS-SUBTILIS

Competence development and sporulation in B. subtilis are partly contr olled by peptides that accumulate in culture medium as cells grow to h igh density. We constructed two genes that encode mature forms of two different signaling molecules, the PhrA peptide that stimulates sporul ation, and CSF, the competence- and sporulation-stimulating factor. Bo th pentapeptides are normally produced by secretion and processing of precursor molecules. The mature pentapeptides were functional when exp ressed inside the cell, indicating that they normally need to be impor ted to function. Furthermore, at physiological concentrations (10 nM), CSF was transported into the cell by the oligopeptide permease encode d by spoOK (opp). CSF was shown to have at least three different targe ts corresponding to its three activities: stimulating competence gene expression at low concentrations, and inhibiting competence gene expre ssion and stimulating sporulation at high concentrations.