30S
A ribosome is made up two main constituent subunits, the larger 50S subunit and the smaller 30S subunit. [1]The 30S subunit is found bound to the newly translated mRNA molecule. This then allows the 50S subunits to bind, forming the full 70S ribosome combination, and two tRNA molecules to attach to the recognition codons. [2] Both the 30S and 50S subunits contain three binding sites: A (aminoacyl), P (Peptidyl) and E (exit).