Some bacterial and most organelle genomes do not encode the full set of 32 tRNA species required to read all codons according to Crick's wobble rules. 'Superwobble', in which a tRNA species with an unmodified U in the wobble position reads all four nucleotides in the third codon position, represents one possible mechanism for how a reduced tRNA set could still suffice. We have tested the superwobble hypothesis by producing knockout mutants for the pair of plastid glycine tRNA genes. Here we show that, whereas the tRNA gene with U in the wobble position is essential, the gene with G in this position is nonessential, demonstrating that the U-containing anticodon can indeed read all four glycine triplets. We also show that the price for superwobbling is a reduced translational efficiency, which explains why most organisms prefer pairs of isoaccepting tRNAs over the superwobbling mechanism.
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We thank the MPI-MP Green Team for plant care and cultivation and S. Ruf for helpful discussion and advice. We are grateful to J. Pieritz and J. Kehr for help with mass spectrometric protein sequencing. M.R. is the recipient of a fellowship from the Deutscher Akademischer Austauschdienst (DAAD, Germany) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil). This research was financed by the Max Planck Society and a grant from the Deutsche Forschungsgemeinschaft.
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Rogalski, M., Karcher, D. & Bock, R. Superwobbling facilitates translation with reduced tRNA sets. Nat Struct Mol Biol 15, 192–198 (2008). https://doi.org/10.1038/nsmb.1370
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