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Dysfunction of nuclear-cytoplasmic transport systems has been associated with many human diseases. Thus, understanding of how functional this transport system maintains, or through dysfunction fails to maintain remains the core question in cell biology. In eukaryotic cells, the nuclear envelope (NE) separates the genetic transcription in the nucleus from the translational machinery in the cytoplasm. Thousands of nuclear pore complexes (NPCs) embedded on the NE selectively mediate the bidirectional trafficking of macromolecules such as RNAs and proteins between these two cellular compartments. In this book, the authors integrate recent progress on the structure of NPC and the mechanism of nuclear-cytoplasmic transport system in vitro and in vivo.
In eukaryotic cells, the nuclear genome and its transcriptional apparatus is separated from the site of protein synthesis by the nuclear envelope. Thus, a constant flow of proteins and nucleic acids has to cross the nuclear envelope in both directions. This transport in and out of the nucleus is mediated by nuclear pore complexes (NPCs) and occurs in an energy and signal-dependent manner. Thus, nucleocytoplasmic translocation of macro molecules across the nuclear envelope appears to be a highly specific and regulated process. Viruses that replicate their genome in the cell nucleus are therefore forced to develop efficient ways to deal with the intracellulZlr host cell transport machinery. Historically, investigation of Polyomavirus replication allowed identification ofsequences that mediate nuclear import, which led subsequently to our detailed understanding of the cellular factors that are involved in nuclear import. Transport ofmacromolecules in the opposite direction, however, is less well understood. The investigation of retroviral gene expression in recent years pro vided the first insights into the cellular mechanisms that regulate nuclear export. In particular, the detailed dissection of the function of the human immunodeficiency virus type I (HIV-I) Rev trans-activator protein identified CRMI, as a hona fide nuclear export receptor. CRM I appears to be involved in the nucleocytoplasmic translocation of the vast majority of viral and cellular proteins that have subsequently been found to contain a Rev-type leucine-rich nuclear export signal (NES).
The exchange of information and matter between cell nucleus and cyto­ plasm is an intriguing aspect of the eukaryotic cell which has attrac­ ted the cell biologists' attention for many decades. Nevertheless, the elucidation of nucleocytoplasmic transport is still in a stage where questions can be more easily formulated than answered. Considering the explosive progress in molecular biology, the somewhat prodromal stage of nucleocytoplasmic transport studies may seem astonishing. However, the situation becomes immediately intelligible if technical aspects are taken into consideration. Nucleocytoplasmic transport is a func­ tion of the living cell and the development of suitable in-vitro sys­ tems proved to be difficult. Recently, novel techniques for measuring molecular transport in single cells have been developed. Substantial proqress has been also achieved by gene technology. In this situation a 'Workshop on Nucleocytoplasmic Transport' was held at the Deutsches Krebsforschungszentrum (German Cancer Research Center), Heidelberg, Federal Republic of Germany. A brief yet essentially complete picture of the field and its prospects was sought. The present book contains the proceedings of this work­ shop. The book is organized in the following manner: - Historical dimensions of the field are illuminated by Brachet. - Techniques for single-cell studies are reported by Engelhardt et al., Garland & Birmingham, Krafft et al., Feldherr, Neuhaus & Schweiger, Riedel et al., Edstrom, and Trendelenburg et al .. - The structure and biochemistry of the nuclear envelope is discussed by Milligan, Maul & Schatten, Krohne & Benavente, and Dreyer et al ..
The nuclear pore complex (NPC) is one of the largest known protein structures in the cell. Evolutionarily conserved in eukaryotes ranging from fungi to plants and animals, the NPC is the main transporter of molecules between the cell cytoplasm and nucleus. Maintaining the proper compartment-specific localization of proteins and RNA is crucial for normal cell function, and the nuclear pore accomplishes this task both robustly and efficiently. Over the past several decades, insight into the composition, organization, structure, and mechanism of the NPC has been gradually teased out through careful experimentation. However, many questions about the pore's function remain unanswered. In this dissertation, I describe efforts aimed at elucidating several aspects of the NPC. First, I investigate the transport properties of the pore, specifically looking at how the nuclear transport receptor importin-[beta] and the Ran GTPase interact not only with each other but also how they may affect the pore itself. The nucleoporin Nup153 is identified as an important player in the nuclear transport process which binds strongly to importin-[beta] in a Ran-sensitive manner. Using multiple experimental techniques, the properties of importin-[beta], and Nup153's interactions are characterized and shown to be capable of modulating the selective permeability barrier of the NPC. Next, I examine how members of a major class of nuclear pore proteins, the scaffold nucleoporins, are both structurally and functionally similar to the karyopherin family of soluble nuclear transport receptors. Structures of the proteins Nup188 and Nup192 are analyzed and shown to resemble those of karyopherins. Furthermore, in vitro assays indicate that at least a subset of the scaffold nucleoporins behave functionally as transport receptors, hinting at an evolutionary relationship between these two important classes of proteins. Finally, a calcium-mediated phenomenon affecting the permeability of the NPC is explored. I show that certain cytosolic proteases are activated by millimolar concentrations of calcium ion which leads irreversibly to an increase in the nuclear pore's permeability to large molecules. A model for physiological pathways implicated in this effect is proposed.
Delivery of therapeutic proteomics and genomics represent an important area of drug delivery research. Genomics and proteomics approaches could be used to direct drug development processes by unearthing pathways involved in disease pathogenesis where intervention may be most successful. This book describes the basics of genomics and proteomics and highlights the various chemical, physical and biological approaches to protein and gene delivery. Covers a diverse array of topics from basic sciences to therapeutic applications of proteomics and genomics delivery Of interest to researchers in both academia and industry Highlights what’s currently known and where further research is needed
Volume 122 of Methods in Cell Biology describes modern tools and techniques used to study nuclear pore complexes and nucleocytoplasmic transport in diverse eukaryotic model systems (including mammalian cells, Xenopus, C. elegans, yeast). The volume enables investigators to analyze nuclear pore complex structure, assembly, and dynamics; to evaluate protein and RNA trafficking through the nuclear envelope; and to design in vivo or in vitro assays appropriate to their research needs. Beyond the study of nuclear pores and transport as such, these protocols will also be helpful to scientists characterizing gene regulation, signal transduction, cell cycle, viral infections, or aging. The NPC being one of the largest multiprotein complexes in the cell, some protocols will also be of interest for people currently characterizing other macromolecular assemblies. This book is thus designed for laboratory use by graduate students, technicians, and researchers in many molecular and cellular disciplines. Describes modern tools and techniques used to study nuclear pore complexes and nucleocytoplasmic transport in diverse eukaryotic model systems (mammalian cells, Xenopus, C. elegans, yeast) Chapters are written by experts in the field Cutting-edge material
In the last decade nucleo-cytoplasmic transport has developed into one of the most active areas of research in cell biology and its significance for cell biology as a whole has been recognized. It has led to elucidation of the mechanisms of major cellular functions such as protein synthesis and cellular differentiation. It is also helping to bring about a synthesis of ultrastructural, biochemical, molecular biological and biophysical approaches to the study of cellular organization and function.