Component of SEC61 channel-forming translocon complex that mediates transport of signal peptide-containing precursor polypeptides across the endoplasmic reticulum (ER) (PubMed:8107851). Component of a ribosome-associated ER translocon complex involved in multi-pass membrane protein transport into the ER membrane and biogenesis (By similarity). The SEC61 channel cooperates with the translocating protein TRAM1 to import nascent proteins into the ER (By similarity). Required for PKD1/Polycystin-1 biogenesis (By similarity). The SEC61 channel-forming translocon complex consists of channel-forming core components SEC61A1, SEC61B and SEC61G and different auxiliary components such as SEC62 and SEC63 (PubMed:10799540, PubMed:10860986, PubMed:8107851). The ribosome-associated ER translocon complex includes SEC61A1, SEC61B, SEC61G, TMCO1, CCDC47, NCLN/Nicalin, NOMO and TMEM147; in the absence of ribosomes, only the complex forms with NCLN/Nicalin, NOMO and TMEM147 remains intact (By similarity). Interacts with TRAM1 (By similarity). Belongs to the SEC61-beta family.