Functions as an RNA ligase, in vitro. The ligation reaction entails three nucleotidyl transfer steps. 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. 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. 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. Exhibits selectivity for single-stranded RNA substrates and may not have nick-sealing activity on double-stranded DNA-RNA hybrids. May play a role in maintaining RNA integrity under stress conditions, for example in response to reactive oxygen species (ROS).