This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: CRISPR may be a powerful technology for gene editing, but the system existed in bacteria long before scientists began using it. For billions of years, CRISPR has acted as a natural immune system in bacteria and other microbes, helping defend them against invading viruses.
But now, two new studies, published in Science, describe a similar RNA-guided system that originated in the viruses themselves and appears to be a precursor to CRISPR. While scientists can manipulate these mechanisms to make precise changes to DNA to treat disease and improve crops, they still aren't sure exactly how the first CRISPR-like immune systems evolved. CRISPR systems use RNA guides to find matching DNA sequences and can be programmed by changing the sequence of the guide RNA.
The origins of CRISPR's core RNA-binding proteins have been especially unclear. The authors of the first study—most of whom are also involved in the second study—write, "CRISPR-Cas systems are divided into two classes on the basis of their effector proteins. Class 1 systems, the more abundant of the two, are thought to have evolved first.
Their defining feature is the presence of repeat-associated mysterious proteins (RAMPs) that oligomerize on the CRISPR RNA (crRNA) to form the RNA-guided effector complex. RAMPs are among the most conserved and ancient features of CRISPR-Cas, proposed to date back to the last universal common ancestor." The team decided to trace where RAMPs came from to find the evolutionary origins of CRISPR-Cas systems. Using a structure-based approach to search for RAMP-like proteins, the team identified an RNA-binding protein they call Viral interference programmable repeat (VIPR).
VIPR was found in bacterial and viral genomes along with a small noncoding RNA, called vrRNA, which acts as the guide RNA. The team says that natural VIPR targets frequently occurred in rival bacteriophages, which are a specialized type of virus that exclusively infects, replicates inside and destroys bacteria. This seems to point to an ancient "arms race" between viruses.
The researchers say that the VIPR system likely arose as a way for viruses to inactivate each other when competing for control inside the bacteria they had invaded. The team thinks that bacteria may have co-opted VIPR systems used by invading viruses and adapted them for host defense. Eventually, this evolved into the CRISPR system found in bacteria.
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