PNKP_ligase is a classical ligase nucleotidyltransferase module of bacteria. PNKP (polynucleotide 5'-kinase/3'-phosphatase) is the end-healing and end-sealing component of an RNA-repair system present in diverse bacteria from ten different phyla. RNA breakage by site-specific 'ribotoxins' is an ancient mechanism by which microbes respond to cellular stress and distinguish self from non-self. Ribotoxins are trans-esterifying endonucleases that generate 5'-OH and 2',3' cyclic phosphate termini. Repair of this type of RNA damage is feasible via sequential enzymatic end-healing and end-sealing steps [1].

1: The adenylyltransferase domain of bacterial Pnkp defines a unique RNA ligase family. Smith P, Wang LK, Nair PA, Shuman S; Proc Natl Acad Sci U S A. 2012;109:2296-2301. PMID:22308407