Component of SEC61 channel-forming translocon complex that mediates transport of signal peptide-containing precursor polypeptides across the endoplasmic reticulum (ER) (PubMed:12475939, PubMed:22375059, PubMed:29719251, PubMed:32814900, PubMed:28782633). Forms a ribosome receptor and a gated pore in the ER membrane, both functions required for cotranslational translocation of nascent polypeptides (PubMed:22375059, PubMed:29719251, PubMed:28782633). May cooperate with auxiliary protein SEC62, SEC63 and HSPA5/BiP to enable post-translational transport of small presecretory proteins (PubMed:22375059, PubMed:29719251). Component of a ribosome-associated ER translocon complex involved in multi-pass membrane protein transport into the ER membrane and biogenesis (PubMed:32820719). The SEC61 channel cooperates with the translocating protein TRAM1 to import nascent proteins into the ER (PubMed:8616892). Controls the passive efflux of calcium ions from the ER lumen to the cytosol through SEC61 channel, contributing to the maintenance of cellular calcium homeostasis (PubMed:28782633). Plays a critical role in nephrogenesis, specifically at pronephros stage (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 (By similarity). 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 (PubMed:32820719). Localizes exclusively in granular structures in the endoplasmic reticulum (ER). Expressed in proximal and distal tubules in kidney (at protein level). The disease is caused by variants affecting the gene represented in this entry. Defects in SEC61A1 may be a cause of autosomal dominant hypogammaglobulinemia, resulting in severe recurrent infections, mainly of the respiratory tract. Disease onset is mostly in the first year of life. Affected subjects manifest reduced antibodies production by plasma cells, in the presence of normal subpopulations of B and T cells in the peripheral blood. Patients respond well to immunoglobulin replacement therapy. Belongs to the SecY/SEC61-alpha family.