Required for the post-translational delivery of tail-anchored (TA) proteins to the endoplasmic reticulum (ER) (PubMed:21444755, PubMed:23041287, PubMed:24392163, PubMed:27226539). 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:21444755, PubMed:23041287, PubMed:24392163, PubMed:27226539). Required to ensure correct topology and ER insertion of CAMLG (PubMed:31417168, PubMed:32187542). {ECO:0000269|PubMed:21444755, ECO:0000269|PubMed:23041287, ECO:0000269|PubMed:24392163, ECO:0000269|PubMed:27226539, ECO:0000269|PubMed:31417168, ECO:0000269|PubMed:32187542}. This is the function of GET1 (guided entry of tail-anchored proteins factor 1, Ensembl gene identifier ENSG00000182093).