Aminoacylation has generally been considered to be the final stage determining translational accuracy (reviewed in Parker, 1989; Kurland, 1992; Farabaugh, 1993) . However, in the case of tRNA Gln charged with glutamate in the chloroplast, Glu-tRNA Gln is rejected by an elongation factor so that the chloroplast translation machinery does not employ the mischarged aminoacyl-tRNA (Stanzel et al., 1994) . It is likely that this is an exceptional case due to the lack of glutamyl-tRNA synthetase in the chloroplast.