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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    some mutants resistant to spectinomycin show this behaviour (both strepto mycin and spectinomycin act on proteins of the 30S subunit, which may be mutated to alter the response of the bacterium to the antibiotic). Some of these mutants show a reduction in synthesis of both 50S and 30S subunit and accu mulate all of their precursors. Figure 4.4 shows the presence of 43S, 32S, 26S, 21S particles in spc- m24 cells. Others have few 50S subunits and no 30S subunits and accumulate 32S and 21S, and possibly also 26S precursor particles; a third class has reduced synthesis of 50S and probably also 30S subunits and accumulates both the 43S and 26S precursors. This implies that the assembly of the 50S subunit may depend on the ability of the proteins of the 30S subunit to associate properly with 16S rRNA to form the 30S particle. A general observation which supports this idea is that all sad mutants which abolish 30S assembly also inhibit 50S assembly, although spc-m.2A\ has reduced synthesis of both 50S and 30S subunits; accumulates 43S and 32S pre cursors to 50S subunits (which contain 23S rRNA) and 26S and 21S precursors to 30S subunits (which contain 17S rRNA). The 32S and 26S precursors form broad peak which overlaps the usual 30S position. spc- 49 : fails to synthesise both 50S and 30S sub- units and instead accumulates 28S pre cursors containing 23S rRNA (equivalent to the usual 30-32S particles) and 21S precursors containing 17S rRNA. fractions on gradient 14 C reference of 50S and 30S subunits H 3 label of mutant cells at 20°C Figure 4.4: Ribosome precursor particles accumulated at low temperature by two mutants in the spectinomycin-resistant class. Data of Nashimoto and Nomura (1970)