FIG. 4.
Possible model for indole signaling in E. coli. The tnaAB operon is depicted and is activated by CRP-cAMP as nutrients are depleted. This results in indole production via the TnaA (tryptophanase) enzyme. The indole is secreted and acts as an extracellular signal. The components of the signal response pathway are unknown and are indicated by a question mark.
