ATPase required for the post-translational delivery of tail-anchored (TA) proteins to the endoplasmic reticulum. Recognizes and selectively binds the transmembrane domain of TA proteins in the cytosol. This complex then targets to the endoplasmic reticulum by membrane-bound receptors GET1/WRB and CAMLG/GET2, where the tail-anchored protein is released for insertion. This process is regulated by ATP binding and hydrolysis. ATP binding drives the homodimer towards the closed dimer state, facilitating recognition of newly synthesized TA membrane proteins. ATP hydrolysis is required for insertion. Subsequently, the homodimer reverts towards the open dimer state, lowering its affinity for the GET1-CAMLG receptor, and returning it to the cytosol to initiate a new round of targeting. May be involved in insulin signaling. Homodimer (By similarity). Component of the Golgi to ER traffic (GET) complex, which is composed of GET1/WRB, CAMLG/GET2 and GET3/TRC40 (PubMed:21444755, PubMed:23041287, PubMed:24392163, PubMed:32910895). Within the complex, CAMLG and GET1 form a heterotetramer which is stabilized by phosphatidylinositol binding and which binds to the GET3 homodimer (PubMed:32910895). Interacts with CAMLG (via N-terminus) (By similarity). GET3 shows a higher affinity for CAMLG than for GET1 (PubMed:24392163). Interacts with SERP1 and SEC61B (PubMed:17382883, PubMed:18477612). Expressed in the epithelial cells of the liver, kidney, and stomach wall, in the adrenal medulla, in the islet cells of the pancreas, in the red pulp of the spleen, and in cardiac and skeletal muscle. Belongs to the arsA ATPase family.