psm regulation in "s. aureus" is primarily controlled by the "agr" system. the exact mechanism of regulation differs from other "agr" controlled toxins, which are controlled by the "agr" effector molecule rnaiii. psms, however, are controlled by direct binding of agra to the promoter region. psm-mec rna has been implicated in the regulation of the agr system and as a result can influence the expression of other psms. in addition to the agr system, sara as well as luxs have both been implicated in psm control, with mutations in either system showing decreased levels of psm production. in addition the mgra system has been shown to alter biofilm formation, via surpression of psms. the environment "s. aureus" is exposed to has been demonstrated to play a role in psm expression. in intracellular environments it has been shown that psm production is increased.