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X-ray (2.3 Å)
Crystal structure of the homo sapiens cytoplasmic ribosomal decoding a site
Kondo J, Urzhumtsev A, Westhof E (2006): "Two conformational states in the crystal structure of the Homo sapiens cytoplasmic ribosomal decoding A site." Nucleic Acids Res., 34, 676-685. doi: 10.1093/nar/gkj467.
The decoding A site of the small ribosomal subunit is an RNA molecular switch, which monitors codon-anticodon interactions to guarantee translation fidelity. We have solved the crystal structure of an RNA fragment containing two Homo sapiens cytoplasmic A sites. Each of the two A sites presents a different conformational state. In one state, adenines A1492 and A1493 are fully bulged-out with C1409 forming a wobble-like pair to A1491. In the second state, adenines A1492 and A1493 form non-Watson-Crick pairs with C1409 and G1408, respectively while A1491 bulges out. The first state of the eukaryotic A site is, thus, basically the same as in the bacterial A site with bulging A1492 and A1493. It is the state used for recognition of the codon/anticodon complex. On the contrary, the second state of the H.sapiens cytoplasmic A site is drastically different from any of those observed for the bacterial A site without bulging A1492 and A1493.

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