SecB is a chaperone protein used to direct the nascent polypeptide to the translocator protein, SecY. It helps to prevent folding, allowing the polypeptide to be translocated successfully.
SecY is the translocator, producing a pore through which a polypeptide can be transported through. This allows the insertion of the protein into the membrane with a lateral gate. This opens, allowing the protein to be inserted into the membrane.
Stop-transfer sequences, found in the polypeptide being translocated, are recognised by SecY. They induce the insertion of the polypeptide into the membrane. With single-pass membrane proteins, the translocator dissociates from the polypeptide, leaving the single transmembrane domain inserted into the membrane. Start-transfer sequences allow double and multi pass membrane proteins to be inserted into the membrane, causing the translocator to begin translocation again.