The beta subunit of the signal recognition particle receptor (SRP) is a transmembrane GTPase which anchors the alpha subunit to the endoplasmic reticulum membrane [1].

1: The beta subunit of the signal recognition particle receptor is a transmembrane GTPase that anchors the alpha subunit, a peripheral membrane GTPase, to the endoplasmic reticulum membrane. Miller JD, Tajima S, Lauffer L, Walter P; J Cell Biol. 1995;128:273-282. PMID:7844142