Figure 1.

Repression of a single gene. Shown is the level of the target protein (number of molecules) versus time: transcriptional regulation (dashed line), post-translational regulation by protein–protein interaction (dashed-dotted line) and post-transcriptional regulation by sRNA (solid line). (A) Both the regulator and the target molecules are present in the cell when the regulation is turned on in response to an external stimulus. The post-translational regulation by protein–protein interaction results in a much faster response than the two other mechanisms. (B) The target protein is present while the regulator is produced in response to an external stimulus. The response mediated by sRNA regulation is the fastest at a time interval immediately after the stimulus takes place.