This book, which results from the dramatic increase in interest in the control mechanism employed in gene expression and the importance of the regulated proteins, presents new information not covered in Translational Regulation of Gene Expression, which was published in 1987. It is not a revision of the earlier book but, rather, an extension of that volume witl, special emphasis on mecha nIsm. As the reader will discover, there is enormous diversity in the systems employing genes for translational regulation in order to regulate the appearance of the final product-the protein. Thus, we find that important proteins such as protooncogenes, growth factors, stress proteins, cytokines, lymphokines, iron storage and iron-uptake proteins, and a panorama of prokaryotic proteins, as well as eukaryotic viral proteins, are translationally regulated. Since for some gene products the degree of control is greater by a few orders of magnitude than their transcription, we can state that for these genes, at least, the expression is translationall y controlled. Translational regulation of gene expression in eukaryotes has emerged in the last few years as a major research field. The present book describes mechanisms of translational regulation in bacteria, yeast, and eukaryotic viruses, as well as in eukaryotic genes. In this book we try to provide in-depth coverage by including important examples from each group rather than systematically including all additional systems not described in the previous volume.

Given the accelerated growth of knowledge in the field of gene expression, it seemed timely to discuss current developments in the area of translational reg- ulation of gene expression as well as to evaluate emerging technology. Translational regulation occurs with prokaryotic as well as with eukaryotic messenger RNA (mRNA) in vivo and in vitro. In prokaryotes, through genetic manipulations and mutagenesis, the mechanisms are much better understood, as for example the mechanism of attenuation. In bacteria, different translational efficiencies for the same mRNA may vary by lOOO-fold. Translational regulation was first observed in 1966 with RNA phages of Escherichia coli by Lodish and Zinder. However, translational regulation of proteins from DNA genomes is also well described for bacteria, as for example gene 32 protein of bacteriophage T4 and E. coli ribosomal proteins. In eukaryotes, the utilization of an individual mRNA species with different efficiencies is poorly understood. For example, mRNA for ribosomal proteins is translationally regulated during Drosophila oogenesis, without any clue to the mechanism involved. It was observed that ribosomal protein mRNA during Drosophila oogenesis and embryogenesis is selectively on or off the polysomes during different developmental stages. In contrast, bacterial ribosomal protein is also translationally regulated by autogenous regulation. The mechanism is well understood and involves binding of the gene product to its transcript in competition with rRNA.