The 54 kDa polypeptide subunit (SRP54) has since been shown to play a central role in the targeting reaction. In an initial step, SRP54 recognizes the hydrophobic N-terminal ‘signal sequences ...

First, three initiation factor proteins (known as IF1, IF2, and IF3) bind to the small subunit of the ribosome ... been linked together in the growing polypeptide chain in the appropriate order.