Variant-specific interaction of kinectin 1 with the multi–tRNA synthetase complex regulates ER sheet organization

Kinectin 1 (KTN1) is an integral endoplasmic reticulum (ER) sheet protein that functions in ER organization and translation elongation. Alternative splicing introduces sequence diversity into the cytoplasmic region of KTN1, but the functional relevance of these variants has remained unclear. Here we show that the multi–tRNA synthetase complex (MSC), composed of eight aminoacyl-tRNA synthetases and three nonenzymatic proteins, specifically interacts with KTN1 in a manner dependent on the alternative exon V2 and glutamine-tRNA synthetase (QARS). Using V2 exon-specific knockout cells and KTN1 knockout cells with variant-specific resucue, we found that the V2 exon is required for KTN1-mediated recruitment of the MSC to the ER, where it promotes the formation of rough ER stacks. These findings define a variant-specific role for KTN1 in anchoring the MSC to the ER, and suggest that this interaction underlies a noncanonical activity of the MSC in regulating ER sheet organization.