Ewen Callaway in Nature:
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 transcribe 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.”
More here.