The N-terminal region of the α-subunit of the TRAP complex has a conserved cluster of negative charges

The α-subunit of the TRAP complex (TRAPα) is a single-spanning membrane protein of the endoplasmic reticulum (ER) which is found in proximity of nascent polypeptide chains translocating across the membrane. Here, we demonstrate the widespread occurrence of TRAPα in eukaryotes as indicated by its existence in man, fish and plants. Despite the fact that the sequence homology is much lower than for other proteins in the translocation site, the overall topology, the location of the glycosylation sites and, most interestingly, the distribution of charges are conserved. These data indicate that the TRAP complex has a ubiquitous function.