The magnesium ion dependencies of several of the reaction rates for assembly of the E. coli protein synthesis initiation complex have been determined as the effects of IF-3 (initiation factor 3) on the overall reaction of 30 S and 50 S ribosomal subunits. The reaction kinetics were studied by light-scattering changes as well as by changes in the fluorescence anisotropy of dansylated-IF-3. The full model for treating these processes consists of 4 reactions, 3 of which are thermodynamically independent. Conditions were chosen and techniques were employed that allowed three of the reactions to be studied individually. This allowed the authors to fit, with a single adjustable rate constant, all of the light-scattering changes that occurred upon flowing 30 S and 50 S ribosomal subunits against varying concentrations of both Mg2+ and IF-3. Preparations of IF-3 were found to react toward 30 S subunits with either of two markedly different binding rates. The authors find that the simplest model that explains both the light-scattering and anisotoropy data for all IF-3 experiments is one that includes as a necessary step the association of 30 S-IF-3 with 50 S subunits to form a 70 S-IF-3 complex.
|Original language||English (US)|
|Number of pages||9|
|Journal||Journal of Biological Chemistry|
|Publication status||Published - Dec 1 1982|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology