UASt regulatory sequences drive expression of the fusion protein associated with the mouse 'Wld[S]' mutation. The 'Wld[S]' fusion protein is composed of the N-terminal 70 amino acids of Mmus\Ube4b, a unique 18 amino acid domain generated during the fusion event and the full-length sequence of Mmus\Nmnat1. The fusion protein is tagged at the N-terminal end with the extracellular and transmembrane domains of mCD8, resulting in the expressed protein being tethered to the membrane.