Volume 1

Gene expression / Benjamin Lewin.

  • Lewin, Benjamin.
Date:
1974-1977
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Gene expression / Benjamin Lewin. Source: Wellcome Collection.

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    tRNA chain NH O N N CH 2 .0 0 C = 0 R-C-NH 2 Figure 2.3: The 3' terminus of aminoacyl-tRNA. An amino acid is linked through an ester bond to the 3' hydroxyl position of the ribose of the terminal adenylate residue of the polynucleotide chain by cleaving the activation complex with hydroxylamine; when the tryptophan present is labelled with O 18 in its carboxyl group, the label is found in the AMP isolated after the hydrolysis. Direct proof was provided when Kingdon et al. (1958) isolated a complex of tryptophan-AMP. The reaction is quite specific for ATP and no other nucleoside triphosphate can be substituted. Cytoplasmic tRNA becomes labelled with C 14 -amino acids upon incubation in the presence of ATP and the amino acid activating system and Hoagland et al. (1958) suggested that the formation of ATP can be represented by the two reactions : (1) ATP + amino acid + enzyme ► enzyme-amino acid-AMP + PP¡ (2) enzyme-amino acid-AMP + tRNA -» aminoacyl-tRNA + enzyme + AMP This two step mechanism was confirmed when Lagerkvist, Rymo and Waldenstrom (1966) isolated the complex formed in reaction (1) by valine and showed that addition of the appropriate tRNA results in the reaction with amino acid shown in (2). The charging of tRNA with amino acid can therefore be represented as illustrated in figure 2.4 and is discussed in more detail in Chapter 5. A historical review of the discovery of the activation of amino acids has been given by Zamecnik (1969). According to the adaptor hypothesis, it is the nucleotide sequence of the anticodon alone in an aminoacyl-tRNA which recognises its particular codon. Chape ville et al. (1962) confirmed that the only stage in protein synthesis at