Artificial repression looping control by regulated autoinhibition of transcription activator-like effector dimer proteins.

We are interested in artificial gene regulation by exploiting principles learned from lactose repressor (lacI) control of the Escherichia coli lac operon through the formation of tight DNA loops on the order of 100-200 base pairs. We previously showed that appropriately designed DNA target-programmable Transcription Activator-Like Effector dimer (TALED) proteins can produce DNA-looping-dependent gene repression comparable to lacI. Here, we demonstrate regulation of such switches by the principle of controlled repressor autoinhibition. Thus, TALEDs are inhibited by controlled cyclization, dependent on small molecules. Cyclized TALEDs poorly participate in DNA looping. We fit DNA loop length-dependent data with an established thermodynamic model to quantitate these effects. We further demonstrate the ability of small molecules to induce gene expression using this system in actively growing E. coli cells. The resulting designed systems demonstrate regulated gene expression by DNA looping, emulating the lac system but with entirely different molecular components.