The function of RLIG1 (RNA 5'-phosphate and 3'-OH ligase 1, ENSG00000133641) is as follows. Functions as an RNA ligase, in vitro (PubMed:36792600). The ligation reaction entails three nucleotidyl transfer steps (PubMed:36792600). In the first step, the RNA ligase reacts with ATP in the absence of nucleic acid to form a covalent ligase-AMP intermediate and release pyrophosphate (PubMed:36792600). In step 2, the ligase-AMP binds to the nucleic acid and transfers the adenylate to the 5'-PO4 terminus to form an adenylylated intermediate (PubMed:36792600). In step 3, the RNA ligase directs the attack of the 3'-OH on the 5'- phosphoanhydride linkage, resulting in a repaired 3'-5' phosphodiester and release of AMP (PubMed:36792600). Exhibits selectivity for single- stranded RNA substrates and may not have nick-sealing activity on double-stranded DNA-RNA hybrids (PubMed:36792600). May play a role in maintaining RNA integrity under stress conditions, for example in response to reactive oxygen species (ROS) (PubMed:36792600). .