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Figure 4.
Figure 4 Yeast tRNA^Asp acceptor stem in monomer 1 (A) and
monomer 2 (B) showing the U -G mismatches. The tRNA acceptor
stem in monomer 1 is bound to the enzymes and shows a regular
RNA conformation for the backbone dihedral angles  and
 (gauche-/gauche+);
the distance between the phosphorus atoms of G68 and C69 is 5.6
Å. The tRNA molecule in monomer 2 shows no contact between the
acceptor stem and the protein. As a consequence, the dihedral
angles and
are
trans/trans for G68, and the distance between the phosphorus
atoms of G68 and C69 is 6.6 Å. 'Accommodation' of U -G
mismatches has already been observed for the yeast AspRS
-tRNA^Asp complex (equivalent to tRNA 1) and for the free tRNA
(equivalent to tRNA 2). (C) Recognition of the discriminator
base G73 of yeast tRNA^Asp by the E.coli AspRS. The hydrogen
bonds between the protein and the nucleic acid are shown as
yellow dotted lines. They are similar to those observed in the
homologous E.coli AspRS -tRNA^Asp complex.
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