Figure 4.

The types of assays to measure the activity of the T3SA. (a) Transcription-based assays. The activation of T3SAs upregulate the expression of the reporter gene, thus leading to an increased production of the corresponding assay proteins. The relative secretion activity is then estimated by the measurement of the fluorescence or of any other relevant signal emitted by the assay protein (e.g., luminescence, colorimetric, etc.). (b) Secretion-based assay. Upon activation of the T3SA, T3SA substrates fused to a specific tag are secreted. The relative amount and location of the substrates inside host cells or in the extracellular medium are measured with the relevant method, as described in (a).