Peculiar hybrid structures called retrons (image at left; see graphic summary at end) that are half RNA, half single-strand DNA are found in many species of bacteria. Since their discovery around 35 years ago, researchers have learned how to use retrons for producing single strands of DNA in the lab, but no one knew what their function was in the bacteria, despite much research into the matter. In a paper published online on November 5, 2020 in Cell, a Weizmann Institute of Science (Israel) team reports on solving the long-standing mystery. The article is titled “Bacterial Retrons Function in Anti-Phage Defense.” Retrons are immune system "guards" that ensure the survival of the bacterial colony when it is infected by viruses. In addition to uncovering a new strategy used by bacteria to protect themselves against viral infection--one that is surprisingly similar to that employed by plant immune systems--the research revealed many new retrons that may, in the future, add to the genome-editing toolkit. The study, conducted in the Microbial Genomics lab (https://www.weizmann.ac.il/molgen/Sorek/) of Weizman Professor Rotem Sorek of the Institute's Molecular Genetics Department, was led by Adi Millman, Dr. Aude Bernheim, and Avigail Stokar-Avihail in Professor Sorek’s lab. Professor Sorek and his team did not set out to solve the retron mystery; they were seeking new elements of the bacterial immune system, specifically elements that help bacteria to fend off viral infection. Their search was made easier by their recent finding that bacteria's immune system genes tend to cluster together in the genome within so-called “defense islands.” When the researchers uncovered the unique signature of a retron within a bacterial defense island, the team decided to investigate further.
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