A group of researchers from the University of Konstanz has discovered the first human RNA ligase, a protein called C12orf29, that plays a vital role in RNA repair. RNA ligases play a critical role in sealing RNA strands during intron-containing tRNA splicing, tRNA repair, mRNA splicing in the unfolded-protein response, RNA recombination, as well as the biogenesis of circular RNAs. While they are known to play a role in viruses and plants, such enzymes had yet to be identified in vertebrates, including humans.
Across various life forms, proteinaceous RNA ligases are present with distinct catalytic mechanisms. Just like DNA ligases, RNA ligases join 5′-PO4 and 3′-OH termini of RNA via a classic three-step mechanism. These enzymes have been heavily exploited as molecular biology tools in RNA editing and sequencing.
The researchers used various protocols to purify and predict the structure of the unexplored protein, providing evidence that C12orf29 links RNA strands using adenosine triphosphate (ATP). They discovered that C12orf29 catalyzes ATP-dependent RNA ligation via a three-step mechanism, involving tandem auto- and RNA AMPylation.
Using CRISPR/Cas9, the team generated a line of human kidney cells, in which the gene encoding C12orf29 was knocked out. The knockout cells were then treated with varying concentrations of menadione, a K vitamin.
Results showed that KO cells were damaged by low concentrations of menadione, while the wild-type cells were damaged only at significantly higher concentrations, suggesting that C12orf29 protects against oxidative cellular stress. The scientists assumed that a previously hidden human RNA repair mechanism underlies the biological function of C12orf29, but further studies will need to be conducted to examine this mechanism in more detail.
The discovery of C12orf29, the first human RNA ligase, opens up new possibilities for RNA repair pathways. The protective role of C12orf29 against oxidative cellular stress highlights the significance of this protein in maintaining RNA integrity. These findings, published in Nature Communications, could have far-reaching implications in the fields of biochemistry, genetics, and cell biology.