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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    figure 2.19. That protein L7/L12 is an essential part of the GTP hydrolysis site of the ribosome is suggested also by the observation of Highland et al. (1973) that the only antibodies against ribosomal proteins which prevent formation of the complex with G factor and GDP in the presence of fusidic acid are those responding to L7/L12. Two other 50S proteins, L6 and LIO, have been implicated by Schreier et al. (1973) in the GTPase action of the trans lation factor G. Although the GTPase site cannot yet be fully defined, it there fore comprises only a small number of 50S subunit proteins, presumably located in one restriction region of the particle. Maximum GTPase activity is displayed only in the presence also of 30S subunits (see page 71). By testing the ability of 30S subunits lacking certain proteins to stimulate the GTPase activity of 50S subunits, Marsh and Parmeggiani (1973) demonstrated that two of the 30S proteins, S5 and S9, are responsible for the stimulation. These two proteins can be cross-linked by bis-imido esters (see page 150), which supports the concept that they are located close together in a region of the 30S subunit which interacts directly with the 50S subunit; they may therefore form part of the interface between the subunits. Subribosomal Particles of the 30S Subunit Reconstituted 30S particles may be almost as active as native subunits. As table 4.6 shows, Traub and Nomura found that the SP30B proteins are essential for all the catalytic activities of the subunit, for particles reconstituted without this fraction are inactive. The SP30A proteins do not appear to play any indispensable role, although in the presence of the SP30B proteins they stimulate tRNA binding and poly-U directed incorporation activity. Each of the SP30 fractions has been separated into its individual protein components. SP30B comprises five proteins, S3, S5, S9, S10 and S14; the SP30A includes only two proteins, SI and S2. By fractionating the SP30B complement into individual proteins on phos- phocellulose columns, Traub, Soli and Nomura (1968) were able to test each Table 4.6: activities of partially and fully reconstituted 30S subunits of E.coli ribo- somes according to Traub and Nomura (1968a, 1968b) tRNA binding/poly-U particle activity poly-U binding 23S core inactive inactive 23S core + SP30A inactive only weakly active 23S core + SP30B half of activity of fully same as fully reconstituted reconstituted particles particles (lowest line) (lowest line) 23S core + SP30A up to 85 % of activity of highly active + SP30A native 30S subunits