Structure of the 70 S ribosome: implications for movement.

The ribosome is a complex molecular machine, with moving parts, many of which are structural elements of rRNA. We compared the X-ray crystal structures of three different functional states of the 30 S ribosomal subunit - two from crystal structures of the isolated 30 S subunit from the Ramakrishnan group and one from a complex of the 70 S ribosome. Even though all three structures are in what could be called the 'ground state' of the subunit, many conformational differences are found, distributed over the whole structure. A striking example is the undulating movement of the penultimate stem of 16S rRNA, which forms several intersubunit bridges with the 50 S subunit.