Component of the multi-pass translocon (MPT) complex that mediates insertion of multi-pass membrane proteins into the lipid bilayer of membranes (PubMed:32820719, PubMed:36261522). The MPT complex takes over after the SEC61 complex: following membrane insertion of the first few transmembrane segments of proteins by the SEC61 complex, the MPT complex occludes the lateral gate of the SEC61 complex to promote insertion of subsequent transmembrane regions (PubMed:36261522). May antagonize Nodal signaling and subsequent organization of axial structures during mesodermal patterning, via its interaction with NOMO (By similarity). {ECO:0000250|UniProtKB:Q6NZ07, ECO:0000269|PubMed:32820719, ECO:0000269|PubMed:36261522}. This is the function of Ensembl gene identifier ENSG00000125912 (NCLN, nicalin).