Fig. 6. Sequence changes in the loop between transmembrane domains 7 and 8 of Sec61 may improve protein translocation across the ER membrane at low temperature. (A) Sequences of the loop regions from mouse, all fishes and cold-water fishes. Positions of mutations in yeast Sec61p defective in translocation are indicated by asterisks. (B) Sec61 sequences from M. musculus, X. laevis and H. antarticus (AY258259). The transmembrane region is boxed. (C) Adaptations to the cold may indicate that hinge regions (black circles) in the loop are required for a conformational change during protein translocation into the ER.