Involved in protein export. Probably interacts with other proteins to allow the postimport or conservative sorting pathway for inner membrane proteins in plastids. Central subunit of the protein translocation channel SecYE. Consists of two halves formed by TMs 1-5 and 6-10. These two domains form a lateral gate at the front which open onto the bilayer between TMs 2 and 7, and are clamped together by SecE at the back. The channel is closed by both a pore ring composed of hydrophobic SecY resides and a short helix (helix 2A) on the extracellular side of the membrane which forms a plug (By similarity). Part of a second Sec protein translocation apparatus. Interacts probably with SECA2. Predominantly localized to envelope membranes. Ubiquitous. Embryo lethal. Cannot substitute for SCY1. Belongs to the SecY/SEC61-alpha family. Intron retention and frameshift at position 388. Intron retention.