RNA GAME IS ON.....

The gene editing technique CRISPR promises to treat all kinds of genetically-linked conditions, 
but it's so far limited to tweaking DNA, not the RNA that does everything from carrying protein sequence info to regulating gene expression. 

That may change soon, however. Scientists have discovered that a commonplace mouth bacterium (Leptotrichia shahii) can be programmed to break down whatever RNA you want. 

You could rip apart viruses, which are frequently based solely around RNA, or kill a cancer cell by denying it the chance to make vital proteins.

This isn't a cure-all right now. Researchers have to refine their approach before it works in humans, and it's hard to say whether or not this RNA editing will be as effective in practice. As you might surmise, though, the potential is huge. If this works as well as it suggests, you could fight a wider array of illnesses with gene editing, even those that are notoriously 
difficult to treat using conventional methods.

CRISPR DNA EDITITING

The researchers originally identified C2c2 in Leptotrichia shahii in a systematic search for previously unidentified CRISPR systems within diverse bacterial genomes. For the present study, the team focused on C2c2, as its sequence contained two copies of a domain—called ­higher eukaryotes and prokaryotes nucleotide-binding (HEPN)—which, thus far, has only been found in RNases.

The group first tested whether C2c2 could be used to provide E. coli immunity against an RNA phage. When the team introduced L. shahii C2c2 locus and RNA phage-specific spacer sequences into E. coli via a plasmid, the bacteria continued to proliferate. E. coli containing the C2c2 locus and control spacer sequences not found in the phage genome did not grow as well.

Purified C2c2 enzymes from L. shahii are ssRNA-specific, the researchers found; they did not cleave double-stranded RNA or ssDNA in vitro. Tinkering with various ssRNA sequence targets, the researchers also found that the C2c2-CRISPR RNA complex preferentially made cuts at uracil residues and certain  secondary structures of ssRNA.

Mutating the putative catalytic site within either of C2c2’s HEPN domains and introducing the mutated enzyme sequence via a plasmid prevented the protection of E. coli from phage infection, the researchers showed. In vitro, none of the four mutated enzyme versions could cut RNA, suggesting that both HEPN domains are necessary for C2c2 to work.

It is likely that the C2c2 CRISPR system could be manipulated to introduce new functions beyond the cutting of RNA—for example, to knock down gene expression—because a HEPN-inactive C2c2 mutant bound but did not cleave its RNA target, the team noted in its report.

Like Cas9, the researchers also showed that C2c2 could be targeted to knock down expression of non-phage RNA. Unlike Cas9, which cuts DNA only within the sequence dictated by the CRISPR RNA, C2c2 could make cuts within the target sequence and adjacent, nonspecific sequences, depending on the conformation of the RNA molecule and amount of exposed ssRNA, the researchers showed.