Transcription Activator-Like Effectors as Tools for Controlling Bacterial Gene Expression

Novel trans-acting regulatory elements that can readily be redesigned to repress any desired gene of interest have the potential to revolutionize the fields of synthetic biology and metabolic engineering. These elements will facilitate the construction of complex genetic circuits and allow optimization of native gene expression without the need to eliminate native regulatory sequences. One such trans-regulatory element is the class of proteins known as Transcription Activator-Like Effectors (TALEs). These proteins, which were originally identified as bacterial virulence factors, have gained traction in biotechnology applications due to their customizable DNA binding specificity. Here, we demonstrate that a TALE designed to bind the lac operator is able to inhibit both transcription initiation and elongation events in E. coli. We have also expanded the versatility of these transcription factors by creating an inducible TALE system; expression of a protease mediates degradation of an engineered TALE, thereby promoting target gene expression. Understanding the attributes of TALEs as well as other trans-acting regulatory systems, such as CRISPR/Cas and sRNAs, will enable researchers to optimize any genetic system of interest.