Transcription activator-like effectors (TALEs) are found in bacterial plant pathogens, where they act as transcriptional activators in the host plant cell nucleus. The specificity of DNA binding is determined by a central modular array consisting of a series of repeats that are 34 amino acids in length. Each repeat in the array recognizes a particular nucleotide, with the specificity depending on the amino acids present in the repeat variable diresidue (RVD) corresponding to residues 12 and 13 of the repeat. This property can be used to design artificial TALEs that bind to a specific DNA sequence (PMID:24933470). By combining a DNA-binding TALE repeat with another functional domain, different type of tools can be produced for use in experiments. For example, while fusion with a transcription activation domain can produce a transcriptional activator ('driver'), fusion with a nuclease can produce a genome engineering tool that can cut DNA at a particular site.