The interactions of elongation factor 1A (eEF1A) from Saccharomyces cerevisiae with elongation factor 1B␣ (eEF1B␣), guanine nucleotides, and aminoacyl-tRNA were studied kinetically by fluorescence stopped-flow. eEF1A has similar affinities for GDP and GTP, 0.4 and 1.1 M, respectively. Dissociation of nucleotides from eEF1A in the absence of the guanine nucleotide exchange factor is slow (about 0.1 s ؊1 ) and is accelerated by eEF1B␣ by 320-fold and 250-fold for GDP and GTP, respectively. The rate constant of eEF1B␣ binding to eEF1A (10 7 -10 8 M ؊1 s ؊1 ) is independent of guanine nucleotides. At the concentrations of nucleotides and factors prevailing in the cell, the overall exchange rate is expected to be in the range of 6 s ؊1

Unnaturally useful: The ability to incorporate unnatural amino acids into proteins (see scheme) has a significant impact on structure–function studies of proteins. Recently, the technique has been applied to proteins in vivo and in eukaryotic cells, thereby providing great prospects for protein engineering. A basic introduction to the field, together with recent developments and case‐studies, is covered in this Minireview.