Complex sentence: Sec61 is an endoplasmic reticulum (ER) membrane protein translocator (aka translocon) It's a doughnut shaped pore through the membrane with 3 major subunits (heterotrimeric).
Split into simpler sentences: Sec61 is an endoplasmic reticulum (ER) membrane protein translocator (aka translocon). It is a doughnut shaped pore through the membrane with 3 major subunits (heterotrimeric).