PNKP adenylyltransferase domain, C-terminal region
This is a short unique anti-parallel two-helical module with an extended tail peptide. It packs tightly against an extended peptide segment, residues 489-501 in UniProtKB:A3DJ38, near the N-terminus of the NTase domain, pfam16542. 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. The exact function of this C-terminal region is unclear; however, the conformation of the bundles changes on transfer of a PO4 from ATP to AMP.