Acts as component of the Sec62/63 complex which is involved in SRP-independent post-translational translocation across the endoplasmic reticulum (ER) and functions together with the Sec61 complex and bip1 in a channel-forming translocon complex. A cycle of assembly and disassembly of Sec62/63 complex from sec61 may govern the activity of the translocon. sec63 may affect sec61-polypeptide interactions by increasing the affinity of targeting pathways for sec61 and/or by modifying sec61 to allow more efficient polypeptide interaction. May also be involved in SRP-dependent cotranslational translocation (By similarity). Component of the heterotetrameric Sec62/63complex composed of sec62, sec63, sec66 and sec72. The Sec62/63 complex associates with the Sec61 complex to form the Sec complex. May physically associate with bip1 in the endoplasmic reticulum and this interaction may be regulated by ATP hydrolysis (By similarity).