This image shows DNA interacting with a computer-generated model of a TAL protei

Question

This image shows DNA interacting with a computer-generated model of a TAL protein, one of a family of proteins found only in a species of the bacterium Xanthomonas. The bacterium uses proteins like this one to find particular gene sequences in cells of the organisms it infects, such as tomatoes, rice, and citrus fruits. Researchers are excited about working with this family of proteins. Their goal is to generate modified versions that can home in on specific gene sequences. Such proteins could then be used in an approach called gene therapy to "fix" mutated genes in individuals with genetic diseases. Given what you know about DNA structure and considering the image above, discuss how the TAL proteins structure suggests that functions.

Explanation / Answer

The structure shows spiral arrangement of TAL repeats and their interaction with DNA. Each structural repeat forms a pair of alpha helices. These repeats are arranged in a right handed helical arrangement whose dimensions track the major groove of DNA. Within each repeat, the variable residues responsible for DNA recognition are located in the bend separating the two helices. These residues are inserted in the major groove of DNA helix with each TAL repeat contact a single base pair.

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