Back to Shapiro: editing DNA fights off viruses (Evolution)

by David Turell @, Thursday, November 12, 2020, 15:08 (17 days ago) @ David Turell

Some bacteria self-destruct to save the colony:

"For several years, researchers have been adapting retrons—mysterious complexes of DNA, RNA, and protein found in some bacteria—into a potentially powerful way to alter genomes of single cell organisms. Now, biology is catching up, as two groups report evidence that, like CRISPR, retrons are part of the bacterial immune arsenal, protecting the microbes from viruses called phages.

"Last week in Cell, one team described how a specific retron defends bacteria, triggering newly infected cells to self-destruct so the virus can’t replicate and spread to others. The Cell paper “is the first to concretely determine a natural function for retrons,” says Anna Simon, a synthetic biologist at Strand Therapeutics who has studied the bacterial oddities. Another paper, which so far has appeared only as a preprint, reports a similar finding.


"In the 1980s, researchers studying a soil bacterium were puzzled to find many copies of short sequences of single-stranded DNA littering the cells. The mystery deepened when they learned each bit of DNA was attached to an RNA with a complementary base sequence. Eventually they realized an enzyme called reverse transcriptase had made that DNA from the attached RNA, and that all three molecules—RNA, DNA, and enzyme—formed a complex.

"Similar constructs, dubbed retrons for the reverse transcriptase, were found in many bacteria.


"The team then noticed that the DNA encoding retron components often accompanied a protein-coding gene, and the protein varied from retron to retron. The team decided to test its hunch that the cluster of sequences represented a new phage defense. They went on to show that bacteria needed all three components—reverse transcriptase, the DNA-RNA hybrid, and the second protein—to defeat a variety of viruses.


"The researchers concluded that the retron somehow “guards” another molecular complex that is the bacterium’s first line of antiviral defense. Some phages deactivate the complex, which triggers the retron to unleash the membrane-destroying protein and kill the infected cell,


"the group realized that next to the genes coding for a retron in a Salmonella bacterium was a gene for a protein toxic to Salmonella. The team discovered the retron normally keeps the toxin under wraps, but activates it in the presence of phage proteins."

Comment: To repeat: Bacteria edit their DNA to self-destruct and save the colony. I would ask how did this developed? Did bacteria learn this on their own or did it happen by design?

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