( esystem's 'a la carte' process happens...)Jumping gene helps explain immune system's abilities

e system's 'a la carte' process happens is still murky," says Craig. But the a la carte approach provides great diversity from a limited number of choices, whether in the immune system or in a cafeteria. For example, at a cafeteria, one diner could have a meal of mashed potatoes, broccoli and a pork chop, and another French fries, salad and a hamburger, and so on through all the possible combinations of offerings. While the choices aren't as tasty, immune cells select sections of certain genetic instructions in order to make instructions for a protein that will recognize a particular antigen. Machinery snips out unwanted genetic sections and reconnects the leftover ones, creating a unique gene (the cellular equivalent of the diner's meal). Snipping out different sections will lead to a different gene, carrying instructions for a different protein that will recognize a different antigen, and on and on. This a la carte process, known as V(D)J recombination, is similar to the excision of jumping genes, but none had matched one of its characteristic oddities: As the unwanted DNA is being removed, the remaining DNA forms a tiny loop. Unexpectedly, when Hermes is being cut out of the DNA, the leftover DNA also forms a hairpin loop, temporarily doubling back on itself, postdoctoral fellows Liqin Zhou, Ph.D., and Rupak Mitra, Ph.D., discovered in experiments in test tubes and with E. coli bacteria. Although this loop distances Hermes from its well-studied cousins, the Hermes protein still has an important family trait, the researchers report. Colleagues at the National Institutes of Health found that a few key building blocks in the protein's DNA-snipping crevice are identical to those in other jumping genes' proteins, even though the overall sequence is quite different. "Because of its similarities both to V(D)J recombination and to other families of jumping genes, Hermes is the first real link between the two processes," says Craig. "It also is likely to be a good model t
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Source:John Hopkins Medecine


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