Fig. 6.

A two-checkpoint molecular ruler model for tRNA recognition by the T box RNA. The T box RNA is shown in the antitermination (“ON”) state. The RNA is shown as ribbons with tRNA (light blue) docked against stem I and the antiterminator [based on the published NMR structure (44)]. Sequence conservation and known tRNA contacts are colored as in Fig 1. The information checkpoint (1 represents the specifier sequence for tRNA anticodon recognition), geometry checkpoint (2 represents the apical region for recognition of tRNA D-/T-loops 60 Å away), and the antiterminator contact (3) are highlighted with arrows.