text: Gram-positive bacteria that participate in quorum sensing typically use secreted oligopeptides as autoinducers.  Peptide autoinducers usually result from posttranslational modification of a larger precursor molecule.  In many Gram-positive bacteria, secretion of peptides requires specialized export mechanisms.  For example, some peptide autoinducers are secreted by ATP-binding cassette transporters that couple proteolytic processing and cellular export.   Following secretion, peptide autoinducers accumulate in extracellular environments.  Once a threshold level of signal is reached, a histidine sensor kinase protein of a two-component regulatory system detects it and a signal is relayed into the cell.  As with AHLs, the signal ultimately ends up altering gene expression.  Unlike some AHLs, however, most oligopeptides do not act as transcription factors themselves.