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Figure 2.
Interactions with the UAA stop codon in the decoding center
in the RF1 and RF2 termination complexes. (A) Stereoview of the
σ[A]-weighted 3F[obs] − 2F[calc] electron density map of the
stop codon and surrounding elements of RF2 and the ribosome.
Electron density is contoured at 1.0 σ for RF2, and at 1.5 σ
for rRNA and mRNA, and colored yellow (RF1), green (mRNA), and
blue (16S rRNA). (B) Interaction of the hydroxyl group of
Ser-206 of the SPF motif of RF2 with A2 of the stop codon. (C)
Interaction of Thr-216 of RF2 with A3 of the stop codon. (D)
Comparison of the positions of Thr-186 of the PVT motif of RF1
(gray) and Ser-206 of the SPF motif of RF2 (yellow), showing
their different modes of recognition of U1 and A2 of the UAA
stop codon. The structures of the two termination complexes were
globally superimposed. (E) Packing of RF2 around A3 of the UAA
stop codon. Val-203 would be positioned to exclude water from
H-bonding to O6 of guanine, helping to discriminate against
guanine at position 3. The structure model is represented as Van
der Waals surfaces for RF2 (yellow) and mRNA (green); 16S rRNA
is shown in blue.
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