Abstract. GTP has been shown to be required for the translocation of nascent secretory and membrane proteins into the lumen of the endoplasmic reticulum (ER). To date, three components known to be involved in protein translocation, the 54 kDa sub-unit of SRP (SRP54) and both the alpha and the beta subunits of the SRP receptor (SRa and SRβ) have been shown to be GTPases. Here, we briefly review what is known about the role of GTP in protein translocation, and we present a speculative model that incorporates these findings.
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