Essential for tRNA splicing and maturation (PubMed:21209330). Acts by directly joining spliced tRNA halves to mature-sized tRNAs (PubMed:21209330). Joins RNA with 2',3'-cyclic-phosphate or 3'-phosphate ends to RNA with 5'-hydroxy ends (By similarity). 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 (By similarity). Can use zinc ions (PubMed:21209330) (PubMed:21209330). Monomer. 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. Belongs to the RtcB family.