Required for the post-translational delivery of tail-anchored (TA) proteins to the endoplasmic reticulum (PubMed:23041287). Together with CAMLG/GET2, acts as a membrane receptor for soluble GET3/TRC40, which recognizes and selectively binds the transmembrane domain of TA proteins in the cytosol (PubMed:23041287). Required to ensure correct topology and ER insertion of CAMLG (By similarity). Component of the Golgi to ER traffic (GET) complex, which is composed of GET1, CAMLG/GET2 and GET3 (PubMed:23041287). Within the complex, GET1 and CAMLG form a heterotetramer which is stabilized by phosphatidylinositol binding and which binds to the GET3 homodimer (By similarity). Interacts with CAMLG/GET2 (via C-terminus) (PubMed:23041287). GET3 shows a higher affinity for CAMLG than for GET1 (By similarity). Belongs to the WRB/GET1 family.