Aprataxin is a DNA-binding protein that catalyses (among other activities) the 5′ decapping of Gpp-DNA (formed by homologs of RtcB3 from the bacterium Myxococcus xanthus). The enzyme binds the guanylate group to a histidine residue at its active site, forming a covalent enzyme-nucleotide phosphate intermediate, followed by the hydrolysis of the guanylate from the nucleic acid and eventual release. The enzyme forms a 5′-phospho terminus that can be efficiently joined by "classical" ligases. The enzyme also possesses the activitiy of EC 18.104.22.168, adenosine-5′-diphospho-5′-[DNA] diphosphatase and EC 22.214.171.124, DNA-3′-diphospho-5′-guanosine diphosphatase.
Maughan, W.P. and Shuman, S. Characterization of 3′-phosphate RNA ligase paralogs RtcB1, RtcB2, and RtcB3 from Myxococcus xanthus highlights DNA and RNA 5′-phosphate capping activity of RtcB3. J. Bacteriol.197 (2015) 3616–3624. [PMID: 26350128]