RNA Mimicry in the Translational Apparatus

Abstract

Among the first functions attributed to RNA was that of an unstable but indispensable intermediate in the synthesis of β-galactosidase upon addition of lactose to the growth medium of the bacterium Escherichia coli (Jacob and Monod 1961). Further work with bacteria and phages elaborated the role of this RNA, called messenger RNA, in translation and revealed that its synthesis is a step at which gene expression could be regulated in response to different signals. Early work on RNA bacteriophages showed that gene expression can further be regulated at the level of translation and that this involves specific RNA structures (Lodish et al. 1964; Lodish and Zinder 1966). Later, translational regulation by the binding of regulatory proteins to specific mRNAs was also characterized in DNA phages and in E. coli . Translational regulation of a different kind occurs frequently in eukaryotes from yeast to mammals. Here, translation initiation factors are often the target of regulation; but in some instances, regulation occurs by binding of a regulatory protein to specific mRNA structures, as in prokaryotes. Most proteins that regulate gene expression at the transcriptional level have a dedicated regulatory function, i.e., they have no other function in the cell. In contrast, most proteins regulating translation are DNA- or RNA-binding proteins that are primarily involved in other cellular processes. Interestingly, the mechanisms of regulation and the primary roles of these proteins are often related. This relationship was first recognized with bacteriophage T4 gene 32 protein, which is involved in DNA replication, recombination, and repair...