Component of a ribosome-associated endoplasmic reticulum (ER translocon complex involved in multi-pass membrane protein transport into the ER membrane and biogenesis. Together with SEC61 and TMCO1, forms the lipid-filled cavity at the center of the translocon where TMEM147 may insert hydrophobic segments of mutli-pass membrane proteins from the lumen into de central membrane cavity in a process gated by SEC61, and TMCO1 may insert hydrophobic segments of nascent chains from the cytosol into the cavity. Acts as a negative regulator of CHRM3 function, most likely by interfering with its trafficking to the cell membrane. Negatively regulates CHRM3-mediated calcium mobilization and activation of RPS6KA1/p90RSK activity.