Figure 6. Model for the topology of Lag1p and Lac1p.

Lag1p and Lac1p are integral membrane proteins with eight TMDs. The N-terminus and C-terminus are located on the cytoplasmic side of the ER and have dilysine-containing ER retrieval signals on their C-terminus. The positions of the Suc2A topological-reporter cassette and fXa-protease-cleavage site insertions are indicated by arrowheads. The numbers refer to the amino acid at which the insertions were fused. The region of the Lag motif, which is indicated in black, is expanded in a box. Most of the Lag motif is predicted to be embedded in the membrane. His²⁵⁵, His²⁵⁶ and Asp²⁸³ are conserved only among Lag1 homologues, not in TRAM, and are essential for the function of Lag1p in vivo (black circles).