Translational repression mechanisms in prokaryotes

Translational repression results from a complex choreography of macromolecular interactions interfering with the formation of translational initiation complexes. The relationship between the rate and extent of formation of these interactions to form repressed mRNA complexes determines the extent of repression. A novel analysis of repression mechanisms is presented here and it indicates that the reversibility of repressed complex formation influences the steady state balance of the distribution of translationally active and inactive complexes and therefore has an impact on the efficiency of repression. Reviewed here is evidence for three distinct translational repression mechanisms, regulating expression of the transcription factor sigma(32), threonine tRNA synthetase and ribosomal proteins on the alpha operon in Escherichia coli. Efficient regulation of expression in these systems makes use of specific mRNA structures in quite different ways.