A human RNA ligase that operates via auto- and RNA-AMPylation

Different forms of life are known to express RNA ligases that catalyse the condensation of a 3’-hydroxy group and a 5’-terminal phosphate of RNA. No such RNA ligases have yet been identified in vertebrates. Here, we report that the hitherto uncharacterised human protein chromosome 12 open reading frame 29 (C12orf29), which we identified by a chemical proteomics approach, is a 5’-3’ RNA ligase. C12orf29 catalyses RNA ligation via auto-AMPylation of a critical lysine residue by using ATP as a cosubstrate and subsequent AMP transfer to the 5’-phosphate of an RNA substrate followed by phosphodiester bond formation. Studies at the cellular level reveal the involvement of C12orf29 in maintaining RNA integrity upon cellular stress induced by reactive oxygen species. These findings highlight the importance of RNA ligation for cellular fitness.