The two evolutionary well-conserved histidine residues, His66 and His11 8, of Escherichia coli elongation factor Tu have been subjected to mutational analysis. The two histidines have each been replaced by alanines, denoted H66A and H11 8A, respectively. His118 has also been substituted by glutamate, H11 SE. The three mutants have been characterized with respect to thermostability, GTPase activity and affinity for aminoacylated tRNA. Most conspicuously, the tRNA affinity is reduced or almost abolished. k-, for dissociation of the ternary complex increases by factors of 14, 40 and 48 for H66A, H118A and H118E, respectively, when compared to the wild type. The halflives for the non-enzymic deacylation of aminoacylated tRNA in the ternary complex are 391, 107, 69, 54 and 61 min for wild type, H66A, H118A, H118E and free aminoacylated tRNA, respectively. The Kd is about 20-times higher for H66A compared to wild type.Our results strongly suggest that His66 and His118 play major roles in stabilization of the ternary complex.Elongation factor Tu (EF-Tu) from Escherichia coli is a monomeric protein consisting of 393 amino acid residues, and with a molecular mass of 43 kDa. During the elongation step in protein biosynthesis EF-Tu promotes the binding of aminoacyl-tRNA to the A-site of the programmed ribosome in the process of decoding the mRNA [l]. In its active conformation with GTP as a cofactor, EF-Tu has a high affinity for aminoacyl-tRNA with equilibrium dissociation constants in the range of 10-'M [2], the affinity for non-acylated tRNA being several orders of magnitudes lower [3].The low intrinsic GTPase activity of EF-Tu is stimulated on the ribosome when EF-Tu is present in the form of a ternary complex with GTP and aminoacyl-tRNA. Upon GTP hydrolysis EF-Tu undergoes a conformational change to a GDP form with negligible affinity for aminoacyl-tRNA. The exchange factor EF-Ts catalyses the replacement of GDP with GTP and thus completes the cycle.The crystal structure of E. coli EF-Tu in complex with GDP has been determined at high resolution [4] and so has the structure of EF-Tu :GTP from the thermophilic bacteria Thermus aquaticus and Thermus thermophilus [5, 61. Theoretical speculations about the biochemical nature of the important intermediate in the elongation process, the ternary complex, has brought about many interesting studies over the last two decades [7, 81. No unequivocal determination of macromolecular recognitory interaction sites has so far been established. To map the interaction points of EF-Tu and aminoacyltRNA different chemical modification studies have been applied in addition to cross-linking and site-directed mutagenesis studies.Modification studies of Cys81 indicated that this residue took part in tRNA binding [9, 101. This conclusion could not, however, be confirmed by mutagenesis studies [11].In three different studies [12-141 several lysine and arginine residues have been indicated to be involved in tRNA binding, in particular Lys2, Lys4, and Lys263. As EF-Tu is expected to recognize...

This paper is one of the first to investigate mobility in overall health using high‐quality administrative data. The attractiveness of this approach lies in objective health measures and large sample sizes allowing twin analyses. I operationalize health mobility by a variety of statistics: rank–rank slopes, intergenerational correlations (IGCs) and sibling and identical twin correlations. I find rank–rank slopes and IGCs in the range 0.11–0.15 and sibling correlations in the range 0.14–0.20. Mobility in health is thus relatively high, both when compared to similar US‐based studies, and when contrasted with outcomes such as educational attainment and income. Comparing sibling and identical twin correlations with parent–child associations confirms earlier findings in the literature on equality of opportunity, namely that sibling correlations capture far more variation than traditional IGCs. I conclude that 14%–38% of the variation in individual health outcomes can be attributed to family background and genes, factors which the individual cannot be held accountable for. This finding suggests that simple parent–child associations may be a poor metric for measuring health mobility.

Two residues of Escherichia coli elongation factor Tu involved in binding of aminoacyl-tRNA were identified and subjected to mutational analysis. Lys-89 and Asn-90 were each replaced by either Ala or Glu. The four single mutants were denoted K89A, K89E, N90A, and N90E, respectively. The mutants were characterized with respect to thermal and chemical stability, GTPase activity, tRNA affinity, and activity in an in vitro translation assay. Most conspicuously tRNA affinities were reduced for all mutants. The results verify our structural analysis of elongation factor Tu in complex with aminoacyltRNA, which suggested an important role of Lys-89 and Asn-90 in tRNA binding. Furthermore, our results indicate helix B to be an important target site for nucleotide exchange factor EF-Ts.Also the mutants His-66 to Ala and His-118 to either Ala or Glu were characterized in an in vitro translation assay. Their functional roles are discussed in relation to the structure of elongation factor Tu in complex with aminoacyl-tRNA.

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