text: The expression of genes in the operon is controlled by three differentially regulated promoters, two of which are controlled by RpoS encoded sigma factor σ.
  * csiD :  is σ-dependent and is activated exclusively upon carbon starvation because cAMP-CRP acts an essential activator for σ containing RNA polymerase at the csiD promoter.
  * gabD: is σ -dependent and is induced by multiple stresses.
  * gabD: is σ dependent and is controlled by Nac (Nitrogen Assimilation Control) regulatory proteins expressed under nitrogen limitation.