DEKTV and YVG motifs in the Lsm domain are important for the activity of Scd6, a conserved translation repressor protein

Scd6 is a conserved RGG-motif protein which represses translation by binding eIF4G through its RGG-motif. Lsm and FDF are two other conserved domains present in the protein, however the role of both these domains is unclear. We provide evidence in this report that the Lsm domain is important for the role of Scd6 in translation. Mutant of Scd6 lacking the Lsm domain does not cause overexpression growth defect in a manner comparable to the wild type. Similar results were observed with two distinct point mutants of Scd6 wherein putative RNA-binding motifs DxEKxTV and YVG were mutated. Upon overexpression, the three mutants were defective in inducing formation of P-bodies and stress granules which are conserved sites of translation repression. Importantly localization to granules in response to glucose deprivation and sodium azide stress was defective for Lsm domain mutants indicating that the inability to localize to granules could be a reason for their defective role in translation. Deletion of scd6 impairs Lsm1 foci formation upon glucose deprivation stress which could not be rescued by complementation with Lsm-domain deletion mutant of Scd6 when compared to the full-length protein. Put together, our results highlight the role of Lsm domain and its specific motifs in Scd6 activity and provide crucial insight into its function.