Cistron Specific Translation Control Protein in Escherichia coli

GENE expression may be controlled during translation by ribosomal selection of mRNAs or even individual cistrons. Escherichia coli initiation factors associated with ribosomes affect the binding of ribosomes to mRNA^1,2; initiation factor IF3, for instance, influences the specificity of mRNA-ribosome interaction^3,4. IF3 activity has been separated into several fractions which show various specificities for different mRNA cistrons^4–9. An important problem is the possibility of intracellular changes in IF3 activity^10–12. From uninfected E. coli, we have now isolated a protein which changes the specificity of IF3 toward different mRNAs; we call this interference factor i. Pure factor i binds to IF3 and specifically affects the translation of T4 and MS2 RNA. Whereas the initiation of translation of the MS2 coat protein cistron is inhibited by factor i, the synthetase cistron—when available—is more rapidly initiated in the presence of factor i. The overall translation of T4 mRNA appears unchanged by factor i, but certain cistrons are stimulated at the expense of others. Interfering factors such as factor i could be important in controlling translation in E. coli.