SET7/9 interacts and methylates the ribosomal protein, eL42 and regulates protein synthesis.

Methylation of proteins is emerging to be an important regulator of protein function. SET7/9, a protein lysine methyltransferase, catalyses methylation of several proteins involved in diverse biological processes. SET7/9-mediated methylation often regulates the stability, sub-cellular localization and protein-protein interactions of its substrate proteins. Here, we aimed to identify novel biological processes regulated by SET7/9 by identifying new interaction partners. For this we used yeast two-hybrid screening and identified the large subunit ribosomal protein, eL42 as a potential interactor of SET7/9. We confirmed the SET7/9-eL42 interaction by co-immunoprecipitation and GST pulldown studies. The N-terminal MORN domain of SET7/9 is essential for its interaction with eL42. Importantly, we identified that SET7/9 methylates eL42 at three different lysines - Lys53, Lys80 and Lys100 through site-directed mutagenesis. By puromycin incorporation assay, we find that SET7/9-mediated methylation of eL42 affects global translation. This study identifies a new role of the functionally versatile SET7/9 lysine methyltransferase in the regulation of global protein synthesis.