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Figure 1.
Figure 1. Editing Reactions, Editing Substrates, and
Sequence Conservation in the Editing Domain(A) LeuRS
aminoacylation and editing reactions. Editing reactions are
indicated by the dashed arrows. Although tRNA has been shown to
be a cofactor for pretransfer editing by IleRS (Baldwin and
Berg, 1966), its role in LeuRS editing is unknown.(B) Diagrams
of the analogs used in this work of LeuRS pre- and posttransfer
editing substrates for the case of noncognate norvaline (Nva).
Left: posttransfer substrate analog,
2′-(L-norvalyl)amino-2′-deoxyadenosine (Nva2AA), mimicking
the 3′ end of the aminoacyl-2′-ester Nva-tRNA^Leu. Right:
pretransfer substrate analog,
5′-O-[N-(L-norvalyl)sulphamoyl]adenosine (NvaAMS), a sulfamoyl
analog of norvalyl-adenylate. In each case, the labile ester
linkages were replaced by a nonhydrolyzable amino linkage to
permit structural studies.(C) Alignment of conserved regions
within the editing (CP1) domain of selected LeuRS (L), ValRS
(V), and IleRS (I) enzymes. The “threonine-rich region”
contains two highly conserved threonines (arrowed) discussed in
the text. In the second region, separated by a bracket, a
conserved glycine-rich loop is followed by a completely
conserved aspartic acid (arrowed) that was mutated to alanine.
Abbreviations: Sc, S. cerevisiae; Ce, Caenorhabditis elegans;
Hs, Homo sapiens; Nc, Neurospora crassa; Ec, E. coli; Tt,
Thermus thermophilus; Bs, Bacillus subtilis; Gs, Geobacillus
stearothermophilus; Sa, Staphylococcus aureus; cyt, cytoplasmic;
mit, mitochondrial.
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