Figure 3.

Validation of the switch system: To test the system functionality, several Stl constructs with various DNA-binding abilities were used. Without induction, i.e., in the absence of the Stl expression inducer tetracycline, cells form blue colonies in all cases. Upon the induction of the full-length wild-type Stl, white colonies are formed as Stl is able to fully repress the lacZ gene. Both the truncated Stl C-terminal domain construct and the HTH motif mutant Stl have diminished DNA-binding ability [8] and, as expected, their expression in M. smegmatis leads to the formation of blue colonies. Note that the difference in the number of colonies between variants represents the transformation efficiency.