Figure 2.

Schematic representation of Model II ³. The transitions from State POST1 through State H are the same as those in Fig. 1. From State H, the subsequent reverse intersubunit rotation causes the small ribosomal 30S subunit translocating forward and unwinding mRNA duplex with two active mechanisms. In the first mechanism (from b' to c), the ribosome interacts preferentially with the open form of the mRNA junction and then translocats unhindered, becoming State POST2. In the second mechanism (from b to c), the ribosome breaks the mRNA duplex and translocates forward, becoming State POST2.