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Transcription activator-like effector
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<p>TAL (transcription activator-like) effectors (often referred to as TALEs, but not to be confused with the <a href="/facts/Homeobox/bpvuuw3v">three amino acid loop extension</a> homeobox class of proteins) are <a href="/facts/Protein/Jxmagu3E">proteins</a> secreted by some <a href="/facts/%CE%92-proteobacteria/k6lha8ll">β-</a> and <a href="/facts/%CE%93-proteobacteria/2ISNVT8r">γ-proteobacteria</a>. Most of these are <a href="/facts/Xanthomonad/1CU9U3rS">Xanthomonads</a>. <a href="/facts/Plant_pathogenic/h6DTufWF">Plant pathogenic</a> <i><a href="/facts/Xanthomonas/3meF29Hv">Xanthomonas</a></i> bacteria are especially known for TALEs, produced via their <a href="/facts/Type_three_secretion_system/WL4VW48e">type III secretion system</a>. These proteins can bind <a href="/facts/Promoter_(biology)/YDYBzLfg">promoter</a> sequences in the host plant and activate the <a href="/facts/Gene_expression/alCPohLR">expression</a> of plant genes that aid bacterial infection. The TALE domain responsible for binding to DNA is known to have 1.5 to 33.5 short sequences that are repeated multiple times (tandem repeats). Each of these repeats was found to be specific for a certain base pair of the DNA. These repeats also have repeat variable residues (RVD) that can detect specific DNA base pairs. They recognize plant <a href="/facts/DNA_sequence/hsPsNCQW">DNA sequences</a> through a central repeat domain consisting of a variable number of ~34 amino acid repeats. There appears to be a one-to-one correspondence between the identity of two critical amino acids in each repeat and each DNA base in the target sequence. These proteins are interesting to researchers both for their role in disease of important crop species and the relative ease of retargeting them to bind new DNA sequences. Similar proteins can be found in the pathogenic bacterium <i><a href="/facts/Ralstonia_solanacearum/olyrb5fh">Ralstonia solanacearum</a></i> and <i><a href="/facts/Burkholderia_rhizoxinica/KU0VrgQ8">Burkholderia rhizoxinica</a></i>, as well as yet unidentified marine microorganisms. The term <a href="/facts/TALE-likes/fm2eqdFA">TALE-likes</a> is used to refer to the putative protein family encompassing the TALEs and these related proteins. </p>