Cytoplasmic fate of messenger RNA (Progress in Molecular and Subcellular Biology, 18)

Among all cellular RNA species of the three main types, ribosomal RNA, transfer RNA or messenger RNA, be they from prokaryotic or eukaryotic organisms, the prokaryotic mRNA is unique in that it has no precursor and is synthesized in the same mature form as it is translated into proteins. In fact, ribosomes join the nascent mRNA chain and engage in protein synthesis long before its transcription is complete. Provisions are even made for slowing down the ribo­ somes at some sites to prevent them from catching up with the RNA-polymerase. Of course, such a situation is only possible in the prokaryotic world where there is no such thing as a nuclear mem­ brane physically secluding the transcription process from the cy­ toplasm where translation is restricted. Quite in the opposite extreme, the eukaryotic pre-messenger RNA has to suffer many and sometimes drastic steps of maturation (capping, polyadenylation, splicing, edition) before the decision is made to export it to the cytoplasm. That is where it enters the scope of this book. Once in the cytoplasm, many options are still open to it: its entrance into polysomes may be delayed (as it is in unfertilized eggs) or merely prohibited (ferritin mRNA in iron-starved cells), directed to specific locations within the cytoplasm or be more or less rapidly degraded. During gametogenesis and early development, translational control is probably the most significant level of gene expression. Front Matter....Pages I-XV TOP Genes: A Translationally Controlled Class of Genes Including Those Coding for Ribosomal Proteins....Pages 1-17 RNase L: Effector Nuclease of an Activatable RNA Degradation System in Mammals....Pages 19-34 3 ́ Untranslated Regions of c-myc and c-fos mRNAs: Multifunctional Elements Regulating mRNA Translation, Degradation and Subcellular Localization....Pages 35-63 Cell-Free Systems for Analysis of Cytoplasmic mRNA Turnover....Pages 65-91 Mechanisms for Posttranscriptional Regulation by Iron-Responsive Elements and Iron Regulatory Proteins....Pages 93-115 Interaction Between Iron-Regulatory Proteins and Their RNA Target Sequences, Iron-Responsive Elements....Pages 117-139 Cytoplasmic Fate of Eukaryotic mRNA: Identification and Characterization of AU-Binding Proteins....Pages 141-172 Translational Control by Polyadenylation During Early Development....Pages 173-198 Function and Characterization of Poly(A)-Specific 3 ́ Exoribonucleases....Pages 199-220 Back Matter....Pages 221-224 This book summarizes the current knowledge on a cascade of gene regulation levels which operate in the cytoplasm of eukaryotic cells and which has until recently been poorly understood. While transcriptional control of eukaryotic genes has been extensively researched and the understanding of this process has reached very sophisticated levels, post- transcriptional control has received much less attention. As the contributions in this book demonstrate, not only is post-transcriptional control in eukaryotes better understood, it is now thought to be a major player in gene expression control in a number of key processes, i.e. control of cell proliferation, gametogenesis and early development or cellular homeostasis.