Human RNA ligase 1 as a novel regulator of ribosome function and translation under oxidative stress

Human RNA ligase 1 (Rlig1) is a recently identified human 5′-3′ RNA ligase essential for maintaining 28S rRNA integrity and promoting cell survival under oxidative stress. Although the enzymatic activity of Rlig1 implies a role in RNA maintenance or repair, its broader molecular context remains insufficiently characterised. Here we identify cellular interactors of Rlig1 using affinity enrichment coupled to mass spectrometry in a HEK293 Rlig1-KO model. Our approach revealed several RNA and DNA surveillance, degradation and repair proteins as well as a diverse set of RNA binding and RNA processing enzymes as potential interactors. Notably, ribosomal proteins were highly enriched, suggesting a link between Rlig1 and the translational machinery. Cross-linking coupled to mass spectrometry confirmed that Rlig1 interacts with 80S ribosomes in vitro and preferentially binds the large ribosomal subunit near the 28S rRNA. Polysome profiling corroborated this interaction, as Rlig1 was recruited to ribosomal fractions containing the large ribosomal subunit in response to oxidative stress. Moreover, Rlig1-deficient cells exhibited earlier polysome loss and significantly impaired translational activity compared to their WT counterparts under these conditions. These results highlight a potential novel role for Rlig1 in safeguarding translation during oxidative stress.