Bacterial immunity: a totally new defense (Introduction)

by David Turell , Thursday, May 23, 2024, 23:02 (183 days ago) @ David Turell

Not CRISPR:

https://www.nature.com/articles/d41586-024-01477-8?utm_source=Live+Audience&utm_cam...

"Genetic information usually travels down a one-way street: genes written in DNA serve as the template for making RNA molecules, which are then translated into proteins. That tidy textbook story got a bit complicated in 1970 when scientists discovered that some viruses have enzymes called reverse transcriptases, which scribe RNA into DNA — the reverse of the usual traffic flow.

"Now, scientists have discovered an even weirder twist1. A bacterial version of reverse transcriptase reads RNA as a template to make completely new genes written in DNA. These genes are then transcribed back into RNA, which is translated into protective proteins when a bacterium is infected by a virus. By contrast, viral reverse transcriptases don’t make new genes; they merely transfer information from RNA to DNA.

“'This is crazy molecular biology,” says Aude Bernheim, a bioinformatician at the Pasteur Institute in Paris, who was not involved in the research. “I would have never guessed this type of mechanism existed.”

"Bacteria fend off viruses and other invaders by deploying myriad defences, such as the juggernaut gene-editing system CRISPR. One of the more mysterious defence systems contains the DNA gene for a reverse transcriptase and a short stretch of mysterious RNA without any clear function: the sequence didn’t seem to encode any protein.

***

"To explain this, the authors note that long RNA strands can form hairpin-like shapes, bringing two distant portions close to each other. The researchers found that the K. pneumoniae reverse transcriptase was doing repeated ‘laps’ around the RNA sequence, which was looped over itself like a shoelace, writing the same RNA molecule into DNA many times over. This created a repetitive DNA sequence.

"How scientists are hacking the genetic code to give proteins new powers

"The repeated segments created a protein-coding sequence called an open reading frame. The researchers named this sequence neo, for ‘never-ending open reading frame’, because it lacks a sequence that signals the end of a protein and, therefore, theoretically has no limit. They then found that viral infection triggers the production of the Neo protein, which causes cells to stop dividing.

***

"The discovery that reverse transcriptase — which has previously been known only for copying genetic material — can create completely new genes has left other researchers gobsmacked. “'This looks like biology from alien organisms,” Israel Fernandez, a computational chemist at Complutense University of Madrid, wrote on X.'"

Comment: the only way this can be explained is design. This is highly complex genomic activity.