Phosphorylation of Elp1 by Hrr25 Is Required for Elongator-Dependent tRNA Modification in Yeast

Elongator is a conserved protein complex comprising six different polypeptides that has been ascribed a wide range of functions,but which is now known to be required for modification of uridine residues in the wobble position of a subset of trnas in yeast,plants,worms and mammals. in previous work,we showed that elongator's largest subunit (elp1; also known as iki3) was phosphorylated and implicated the yeast casein kinase i hrr25 in elongator function. here we report identification of nine in vivo phosphorylation sites within elp1 and show that four of these,clustered close to the elp1 c-terminus and adjacent to a region that binds trna,are important for elongator's trna modification function. hrr25 protein kinase directly modifies elp1 on two sites (ser-1198 and ser-1202) and through analyzing non-phosphorylatable (alanine) and acidic,phosphomimic substitutions at ser-1198,ser-1202 and ser-1209,we provide evidence that phosphorylation plays a positive role in the trna modification function of elongator and may regulate the interaction of elongator both with its accessory protein kti12 and with hrr25 kinase. © 2015 abdel-fattah et al.