Survival and proliferation of bacteria depend on their expressing the right amounts of the right genes at the right time. However, what is “right” at any given time-point will vary with the environmental conditions and the specific growth phase. Bacteria often respond to these changing environmental stimuli by switching the expression of specific genes “on” or “off”. To ensure that target gene expression is optimal, will require finetuning of the regulatory parameters that control the switch, and this fine-tuning can affect each individual step of gene expression. In bacteria, gene expression is frequently controlled by proteins that activate or repress transcription by binding to specific DNA sequences close to a promoter. The DNA binding activity of these transcription factors is triggered by small molecules or, less often, by protein-protein interactions. Tet repressor is a paradigm for a bacterial transcription factor that responds directly to an environmental signal by binding a small molecule. TetR regulates transcription of the resistance protein TetA in at least 14 different efflux-type tetracycline resistance determinants found predominantly in Gram-negative bacteria. Repression by TetR has to be tight, because overproduction or constitutive expression of the membrane transporter TetA strongly reduces bacterial fitness. But, at the same time, induction must be sensitive to ensure that TetA is translated before the antibiotic reaches an intracellular level that inhibits translation. Although seemingly conflicting, these requirements are met by the exceptionally high specificity of TetR for its cognate binding site tetO over non-specific DNA and by its unusually high affinity for tetracyclines. Such favorable properties have made TetR a very popular tool for many different applications, including conditional gene expression in both pro- and eukaryotes, overexpression of heterologous proteins or artificial genetic circuits in synthetic biology with highly diverse architectures. So far, all applications using Tet regulation have relied on tetracycline or its analogs as inducers. The recent discovery that peptides can also specifically induce TetR when they are fused to a carrier protein added a new quality to Tet regulation. These inducing peptides, called TIP, bind to the tetracycline-binding pocket of TetR and elicit an allosteric conformational Lomitapide Mesylate change that leads to the complete loss of DNAbinding activity. This turned TetR from an exclusively small-molecule-controlled protein into a downstream effector in a protein signal transduction pathway. Examples of protein-induced regulation of gene expression are not so common in bacteria, but have been found among the major transcription factor families. Information transfer by protein-mediated signal transduction not only introduces new ways to manipulate TetR-based genetic networks in synthetic biology. It also allows to gather proteomic data by determining protein expression profiles after tagging many different proteins with TIP and monitoring their expression by genetic LOUREIRIN-B readout of the TetR-controlled reporter gene. Compared with the intensely studied and well-characterized induction of gene expression by tetracyclines, the parameters for sensitive and efficient control of a Tet-regulated reporter gene by a protein-based inducer are still largely unknown. While the basic functionality of TIP-mediated induction of TetR has been demonstrated in Escherichia coli and in Staphylococcus aureus, major obstacles must still be overcome, if this system is to be used effectively in more sophisticated applications, like those mentioned above. In the examples published so far, efficient induction of TetR was only achieved after strong overproduction of the TIP-containing fusion protein from a multicopy plasmid.