GTP-dependent RNA ligase that is involved in tRNA splicing and RNA repair (PubMed:21224389, PubMed:21757685, PubMed:22045815, PubMed:22730297, PubMed:22474365, PubMed:26858100). Joins RNA with 2',3'-cyclic-phosphate or 3'-phosphate ends to RNA with 5'-hydroxy ends (PubMed:21224389, PubMed:21757685, PubMed:22045815, PubMed:22730297, PubMed:22474365, PubMed:26858100). Also acts as a DNA ligase in case of DNA damage by splicing 'dirty' DNA breaks, characterized by 3'-phosphate (or cyclic-phosphate) and 5'-hydroxy ends that cannot be sealed by classical DNA ligases (PubMed:24218597). a 3'-end 3'-phospho-ribonucleotide-RNA + a 5'-end dephospho-ribonucleoside-RNA + GTP = a ribonucleotidyl-ribonucleotide-RNA + diphosphate + GMP a 3'-end 2',3'-cyclophospho-ribonucleotide-RNA + a 5'-end dephospho-ribonucleoside-RNA + GTP + H2O = a ribonucleotidyl-ribonucleotide-RNA + diphosphate + GMP + H(+) Binds 2 manganese ions per subunit. Monomer. Expression is repressed by RtcR. Ligation proceeds through 3 nucleotidyl transfer steps, with 2',3'-cyclic phosphate termini being hydrolyzed to 3'-P termini in a step that precedes 3'-P activation with GMP. In the first nucleotidyl transfer step, RtcB reacts with GTP to form a covalent RtcB-histidine-GMP intermediate with release of PPi; in the second step, the GMP moiety is transferred to the RNA 3'-P; in the third step, the 5'-OH from the opposite RNA strand attacks the activated 3'-P to form a 3',5'-phosphodiester bond and release GMP (PubMed:22474365, PubMed=26858100). Acts as a DNA ligase by attaching a GMP nucleotide to a DNA 3'-P to form a 'capped' 3' end structure, DNA3'pp5'G. When a suitable DNA 5'-OH end is available, RtcB catalyzes attack of the 5'-OH on DNA3'pp5'G to form a 3'-5' phosphodiester splice junction (PubMed:24218597). Belongs to the RtcB family.