Preface/Front Matter

Abstract

Regulation of gene expression occurs at multiple levels: transcription, messenger RNA processing and stability, translation, and protein modification and turnover. Translational control is defined narrowly as modulation of the efficiency of translation of mRNAs and more broadly to include translation-coupled regulation of mRNA stability. Control at the level of protein synthesis allows cells to respond rapidly to changes in physiological conditions, since activation or repression of mRNAs can occur essentially instantaneously, whereas regulation at the level of transcription entails a considerable time lag before a precursor RNA is processed and mRNA can accumulate or decay in the cytoplasm. Numerous examples of regulation of gene expression at the translational level are now known and serve as the focus of this monograph.

Our understanding of the pathways of transcription and translation is based on experiments that began in the 1950s and identified the major elements involved, such as DNA-dependent RNA polymerase and ribosomes. Whereas early studies of transcription employed largely genetic approaches and were concerned with defining cis-acting DNA sequence elements, characterization of the translational machinery and pathway relied almost exclusively on biochemical methods. Through fractionation of the translational apparatus and reconstitution of active protein synthesis systems in vitro, the major macromolecular components such as tRNAs and soluble factors were identified and characterized. During the 1960s and early 1970s, a detailed pathway of protein synthesis was defined in prokaryotes and that for eukaryotes lagged only a few years behind. Thus, by 1980, the molecular interactions of the major components of protein synthesis