Component of SEC61 channel-forming translocon complex that mediates transport of signal peptide-containing precursor polypeptides across the endoplasmic reticulum (ER) (By similarity). Forms a ribosome receptor and a gated pore in the ER membrane, both functions required for cotranslational translocation of nascent polypeptides (By similarity). The SEC61 channel is also involved in ER membrane insertion of transmembrane proteins: it mediates membrane insertion of the first few transmembrane segments of proteins, while insertion of subsequent transmembrane regions of multi-pass membrane proteins is mediated by the multi-pass translocon (MPT) complex (PubMed:32820719, PubMed:36261522). The SEC61 channel cooperates with the translocating protein TRAM1 to import nascent proteins into the ER (By similarity). {ECO:0000250|UniProtKB:P60058, ECO:0000250|UniProtKB:P61619, ECO:0000269|PubMed:32820719, ECO:0000269|PubMed:36261522}. This is the function of SEC61G (SEC61 translocon subunit gamma, ENSG00000132432).