Figure 3: The C·A mismatch does not form a stable pair in the 70S ribosome-decoding centre.
From: Structural insights into the translational infidelity mechanism
(a,b) The C·A mismatch at the first position of the codon–anticodon duplex in the absence (a) or presence (b) of the queuosine modification in the tRNA anticodon. In a, the left panel shows that A1493 in 16S rRNA prevents strong pairing interactions in the C·A mismatch by constraining its sugar-phosphate backbone by hydrogen bonding. In b, the left and middle panels demonstrate a lack of pairing in the C·A mismatch reflected by the weak electron density signal corresponding to the cytosine base and misshaping of the mini-helical structure due to displacement of the cytosine by queuosine (right). (c) The C·A mismatch at the second position of the codon–anticodon duplex; as in a and b, the left panel depicts conserved A1492 and G530 in 16S rRNA tightening around the mismatch and contorting it. The density maps are contoured at 1.8 σ level. In a–c, the right panels depict overall geometry of the mismatches in the codon–anticodon mini-helices.
