Question

This image shows DNA (grey) interacting with a computer-generated model of a TAL protein (multicolored), one of a family of proteins found only in a species of bacterium Xanthomonas. The bacterium uses proteins like this once to find specific gene sequences in cells of the organisms it infects, such as tomatoes, rice and citrus fruits. Given what you know about DNA structure and considering the image above, discuss how the TAL protein's structure suggests that it functions.

Short answer

The multicolored spiral structure seen in the image is the TAL protein present in the bacterium Xanthomonas. This protein helps to detect the sequences of the host cell. The detection takes place by the interaction of the host DNA structure and the TAL protein.

Step-by-step solution

Definition of DNA 

DNA (deoxyribonucleic acid) consists of nucleic acid bases such as adenine, guanine, thymine, cytosine, and uracil. A and T are purine bases. C and G are the pyrimidine bases. The sugar bases are attached along with a phosphate with nitrogenous bases.

Explanation of TAL protein

TAL proteins are the transcription factors found in certain species of bacterium, such as Xanthomonas (pathogenic bacteria). The transcription factors are the assisting protein that helps the conversion of DNA into RNA.

The work of the TAL protein is unique in that it can identify the DNA sequence of the host, such as tomatoes, rice, and citrus fruits. So, the TAL is an effector molecule present in the pathogenic bacteria to recognize host sequences.

Interaction of host DNA and TAL protein in the bacteria

The TAL protein possesses central tandem repeat domains that have 34 amino acids. There are two hypervariable amino acids present within the central tandem repeat sequences at 12 and 13.

These hypervariable amino acids are the host DNA-specific residues that attach the TAL protein to the host DNA.

In the given figure, the TAL proteins are attached to the specific sites of the DNA confirms that the central tandem repeats have the ability for the TAL protein to target the specific DNA site.