added a model of C73-C74 of the tRNA and residues 342–351 and 375–390 of Aa.LC. The refinement was carried out by conjugate gradient minimization and torsion angle dynamics simulated annealing 30 . Iterative model building and refinement improved the model, resulting in final R work and R free values of 23.0% and 28.7%, respectively. The final model includes two AMPcPP molecules and 79 water molecules. All of the refinement calculations were done with CNS 31 . Refinement statistics are shown in Supplementary Table 1. All of the figures were prepared with the programs Que (http://www.biochem.s.u-tokyo.ac.jp/,ishitani/que/) and PyMol (http:// pymol.sourceforge.net/). In vitro assays Mutations were generated by the QuickChange mutagenesis kit (Stratagene). The mutant proteins were overexpressed and purified as described for the wild-type enzyme. We assayed activity in a solution containing 50 mM glycine (pH 8.5), 10 mM MgCl 2 , 35 mM KCl, 1 mM dithiotheitol, 5% (v/v) glycerol, 0.2 mM tRNA, 10 mM ATP, 100 nM [a- 32 P]ATP (3,000 Ci mol 21 ) and 10 nM enzyme at 50 8C. After the reactions were stopped, the samples were separated by 10% denaturing PAGE. The assay conditions were developed, on the basis of the wild-type Michaelis constant (K m ) values for tRNA (2.3 mM) and ATP (47 mM), to be sensitive enough to evaluate mutant activity. Assays of mutant tRNAs (tRNA-N74N75, where N is A, G, C or U) were done as described above, except that the concentrations of tRNA-N74N75 and ATP were 5 and 250 mM, respectively. Received 6 April; accepted 4 June 2004; doi:10.1038/nature02712. 1. Sprinzl, M. & Cramer, F. The -C-C-A end of tRNA and its role in protein biosynthesis. Prog. Nucleic Acid Res. Mol. Biol. 22, 1–69 (1979). 2. Green, R. & Noller, H. F. Ribosomes and translation. Annu. Rev. Biochem. 66, 679–716 (1997). 3. Kim, D. 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Kawamoto and H. Sakai for help with data collection at SPring-8. This work was supported by Kurata Memorial Hitachi Science and Technology Foundation, Takeda Science Foundation, Foundation of Advanced Technology Institute and a Grant-in-aid for Young Scientists (to K.T.); by Asahi Glass Foundation (to S.F.); by a grant from the Ministry of Education, Culture, Sports, Science and Technology (to N.T.); and by a PRESTO Program grant from Japan Science and Technology and a Naito Foundation grant (to O.N.). Competing interests statement The authors declare that they have no competing financial interests. Correspondence and requests for materials should be addressed to O.N. (onureki@bio.titech.ac.jp). Atomic coordinates have been deposited in the Protein Data Bank under accession number 1VFG. .............................................................. erratum Single-crystal metallic nanowires and metal/semiconductor nanowire heterostructures Yue Wu, Jie Xiang, Chen Yang, Wei Lu & Charles M. Lieber Nature 430, 61–65 (2004). ............................................................................................................................................................................. In Fig. 2b of this Letter, the units of the abscissa should be volts (V). In Fig. 3a, the step labels (3) and (4) should be interchanged. A letters to nature NATURE | VOL 430 | 5 AUGUST 2004 | www.nature.com/nature 704 ©2004 Nature Publishing Group