Discrimination against misacylated tRNA by chloroplast elongation factor Tu

Chloroplast elongation factor Tu was purified from Pisum sativum and the binding properties of glutamylated chloroplast tRNAs were studied by gel-permeation chromatography. Whereas chloroplast Glu-tRNA(Glu) is efficiently bound by this factor, the misacylated Glu-tRNA(Gln) does not interact with chloroplast elongation factor Tu.GTP and is thus efficiently excluded from protein synthesis. Comparison with the behaviour of Escherichia coli elongation factor Tu.GTP shows that this factor, which is not confronted with the in vivo misacylation phenomenon of organelles, binds both Glu-tRNA(Glu) and Glu-tRNA(Gln) from chloroplasts with approximately equal efficiency.