Section I: Biological Importance of GTPase-Driven Switches.- 1 GTPases Everywhere!.- A. Introduction.- B. The GTPase Cycle and the Molecular Switch.- C. Structure of the GTPase Switch.- D. Primary Structures Identify GTPases with Related Functions.- E. Uses of the GTPase Switch: Stoichiometric Activation.- F. Uses of the GTPase Switch: Assembling a Complex.- G. Other Potential Uses of the GTPase Switch.- H. Cascades of GTPases.- I. Perspectives.- References.- 2 Proofreading in the Elongation Cycle of Protein Synthesis.- A. Introduction.- B. General Concepts.- I. Specificity.- II. Proofreading.- C. Parameters of Protein Biosynthesis.- D. EF-Tu-Dependent Kinetic Proofreading.- E. EF-Tu-Independent Error Correction Mechanisms.- I. Peptidyl Transfer.- II. EF-G-Dependent Translocation.- III. Allosteric Linkage Between A and E Sites.- F. Summary.- References.- 3 A New Look at Receptor-Mediated Activation of a G-Protein.- References.- 4 Small GTPases and Vesicle Trafficking: Sec4p and its Interaction with Up- and Downstream Elements.- A. Introduction.- B. The Sec4 Cycle.- I. A Cycle of Sec4 Localization.- II. Intrinsic Properties of Sec4.- III. GTP Binding and Membrane Attachment Are Essential for Sec4 function.- IV. GTP Hydrolysis Is Important for Sec4 function.- C. Accessory Proteins in the Sec4 Cycle.- I. A Specific Sec4 GAP Is Present in Yeast and Mammalian Cells.- II. GDI from Bovine Brain and Yeast Solubilizes Sec4 in a Nucleotide-Specific Fashion.- III. Suppressors from Yeast and Rat Brain Encode Nucleotide Exchange Proteins.- D. A Potential Downstream Effector of Sec4 Function: The Sec8/Secl5 Complex.- References.- 5 Cytoskeletal Assembly: The Actin and Tubulin Nucleotidases.- A. Introduction.- B. The Nucleotidase Cycle in the Polymerization of Actin and Tubulin.- C. Elementary Steps in NTP Hydrolysis on Actin Filaments and Microtubules: The Regulation of Polymer Assembly.- D. Nucleotide and Metal Ion Binding to Actin and Tubulin.- E. Probing the Nucleotidase Mechanism of Actin and Tubulin using AlF4? and BeF3?, H2O.- F. Conclusions.- References.- 6 Dynamin, A Microtubule-Activated GTPase Involved in Endocytosis.- A. Introduction.- B. Structure and Enzymatic Properties.- C. The Drosophila Shibire Gene.- D. Transfection of Dynamin into Cultured Mammalian Cells.- References.- 7 Transmembrane Protein Translocation: Signal Recognition Particle and Its Receptor in the Endoplasmic Reticulum.- A. Introduction.- B. The Signal Recognition Particle and Its Receptor.- C. Protein Translocation Across the Rough Endoplasmic Reticulum Requires GTP.- D. Binding and Hydrolysis of Guanine Ribonucleotides by Signal Recognition Particle and Its Receptor.- E. Site-Directed Mutagenesis of SR?.- F. The Sorting and Targeting Functions of Signal Recognition Particle are GTP Independent.- G. Current Models for GTP Function During Protein Translocation.- References.- 8 GTPases and Actin as Targets for Bacterial Toxins.- A. Introduction.- B. General Features of ADP-Ribosylating Toxins.- C. ADP-Ribosylation of Elongation Factor 2 by Diphtheria Toxin and Pseudomonas aeruginosa Exotoxin A.- I. Introduction.- II. Diphtheria Toxin.- III. Pseudomonas aeruginosa Exotoxin A.- IV. Functional Consequences of the ADP-Ribosylation of Elongation Factor 2.- D. ADP-Ribosylation of G-Proteins.- I. Introduction.- II. Cholera Toxin.- III. Heat-Labile E. coli Enterotoxins.- IV. Functional Consequences of the ADP-Ribosylation of G-Proteins by Cholera- and Heat-Labile E. coli Enterotoxins.- V. Pertussis Toxin.- VI. ADP-Ribosylation of Gi Go, and Gt by Pertussis Toxin.- E. ADP-Ribosylation of Small GTPases.- I. Introduction.- II. C3-Like ADP-Ribosyltransferases.- III. Functional Consequences of the ADP-Ribosylation of Rho Proteins.- IV. ADP-Ribosylation of Small GTPases by Pseudomonas aeruginosa Exoenzyme S.- F. ADP-Ribosylation of Actin.- I. Introduction.- II. Clostridium botulinum C2 Toxin.- III. Other Actin-ADP-Ribosylating Toxins.- IV. Functional Consequences of the ADP-Ribosylation of Actin.- G. Perspectives.- References.- Section II. Structure of the GTPase Switches.- 9 Eukaryotic Translation Factors Which Bind and Hydrolyze GTP.- A. GTPase Factors.- B. Consensus Sequences of GTPases Factors.- C. Evolution of EF-1?.- D. The EF-Tu Family.- E. Structures of the EF-Tu Family.- References.- 10 Heterotrimeric G-Proteins: ?, ?, and ? Subunits.- A. Introduction.- B. Mammalian G-Proteins.- I. ? Subunits.- 1. Isolation of cDNAs and Genomic DNAs.- a) Gs?.- b) Gi?.- c) Go?.- d) Gt? and Ggust?.- e) Gz?.- f) Gq? and G12?.- 2. Comparison of the Amino Acid Sequences.- a) P Region.- b) G? Region.- c) G Region.- d) G? Region.- e) Cholera Toxin ADP-Ribosylation Site.- 3. Sequence Conservation.- 4. Evolutionary Tree.- II. ? ? Subunits.- C. G-Proteins in Lower Eukaryotes.- I. G-Proteins from Saccharomyces cerevisiae.- 1. Two ? Subunits, GPA1 and GPA2.- 2. ? and ? Subunits.- II. G-Proteins from Schizosaccharomyces pombe.- III. G-Proteins from Caenorhabditis elegans.- IV. G-Proteins from Plants.- References.- 11 Molecular Diversity in Signal Transducing G-Proteins.- A. The ? Subunits.- I. Molecular Diversity.- II. ? Subunit Functions.- B. The ? ? Dimers.- References.- 12 Structural Conservation of Ras-Related Proteins and Its Functional Implications.- A. Introduction: The Discovery of Ras and Ras-Related Genes.- B. Sequence Comparisons.- I. The N-Terminal Extension.- II. The Phosphate-Binding Part.- III. The Guanine-Binding Part.- IV. The C-Terminal Extension.- V. The CaaX Motif.- C. Evolutionary Relationships.- I. Construction of a Homology Tree.- II. Insertions and Deletions.- III. Estimation of the Number of Ras-Related Proteins in Mammals.- D. Discussion.- I. Internal Residues.- II. External Residues and Potential Targets for Interacting Proteins.- III. Relation to Other GTPase Families.- IV. Is There a Conserved Functional Mechanism for All Ras-Related Proteins?.- References.- 13 Conformational Switch and Structural Basis for Oncogenic Mutations of Ras Proteins.- A. Introduction.- B. Conformational Switch.- I. Conformational Differences Between GDP- and GTP-Bound Ras Proteins: Switch I and II Regions.- II. Conformational Domino Effect and Frozen Dynamic States.- III. Small Conformational Changes in the Phosphate-Binding Loop, L1.- C. Structural Basis for Oncogenic Mutations.- I. Mutations at Gln-61 and the Stabilization of the Transition State of the ?-Phosphate of GTP.- II. Mutations at Gly-12 and the Stabilization of the Transition State of the ?-Phosphate of GTP.- III. Residues 12 and 13 Form a Type II ?-Turn for Phosphate Binding.- IV. Mutation at Ala-59 and Switch II Conformation.- D. Discussion.- References.- 14 Structural and Mechanistic Aspects of the GTPase Reaction of H-ras p21.- A. Introduction.- B. The Structure of the p21-Triphosphate State.- C. The Structure and Biochemistry of p21 Mutants.- D. The Kinetic Mechanism of the GTPase Reaction.- E. The Kinetic Mechanism of the GAP-stimulated GTPase.- F. GTPase Mechanism.- G. Arguments For and Against the Proposed Mechanism.- H. Role of GAP in the Chemical Mechanism.- I. Conclusion.- References.- 15 Analysis of Ras Structure and Dynamics by Nuclear Magnetic Resonance.- A. Introduction.- B. NMR Studies of Proteins.- I. NMR Structure Determination.- 1. NMR Methods: Larger Proteins.- 2. NMR Resonance Assignments: Application to Ras.- 3. Secondary Structure Determination: Application to Ras.- 4. Tertiary Structure and Structure Refinement.- II. Comparison of Solution and Crystal Structures.- 1. Computer Simulation: Ras·GMPPNP Solution Structure.- 2. Protein Dynamics.- C. Comparison of Full length and Truncated Ras Proteins.- I. Protein Stability: Sample Preparation.- II. Chemical Shift Differences.- III. Selective Isotope Enrichment Studies: Site Specific Probes.- 1. Identification of C-Terminal Peaks.- 2. Internal Dynamics.- 3. Comparison of Intact Ras·GDP and Ras·GMPPCP.- D. Comparison of Ras·GTP, Ras·GTP?S, Ras·GMPPCP and Ras·GDP.- I. Chemical Shift Differences.- E. Kinetic Measurements.- I. Kinetic and Fluorescence Studies.- II. 31P NMR: Ras·GTP Hydrolysis.- III. [1H-15N]-Edited NMR Spectroscopy: GTP Hydrolysis.- F. Conclusion.- References.- 16 Molecular Dynamics Studies of H-ras p21-GTP.- A. Introduction.- B. Methods.- C. Results and Discussion.- I. General Features of the Wild-Type Simulations.- 1. RMS.- 2. Protein-GTP Contacts.- 3. Secondary Structure.- II. Mechanism of Hydrolysis.- References.- Section III: Small Ras - Related GTPases.- A. Control of Growth and Differentiation by the Ras Family.- 17 The Discovery of Ras and Its Biological Importance.- References.- 18 Oncogenic Activation of ras Proteins.- A. Introduction.- B. Oncogenic Versions of Cellular ras Genes Detected in Tumor Cells.- I. Biological Detection of Activating ras Genes.- II. Direct Detection of ras Mutations in Tumor DNA and RNA.- III. Polymerase Chain Reaction Based Approaches to Screening Tumors.- C. Frequent Occurrence of Mutated ras Genes in Human Tumors.- D. ras Activation is Associated with Experimentally Induced Rodent Tumors.- E. Biological Activities of Oncogenic ras Proteins.- I. Malignant Transformation of Established Rodent Fibroblast Cell Lines.- II. ras Requires Cooperation with Other Oncogenes for Transformation of Primary Cells.- III. Induction of Differentiation and Growth Inhibition by Oncogenic ras.- IV. Transgenic Mouse Studies Establish ras Oncogenicity.- F. Structural and Biochemical Consequences of Oncogenic Mutations.- I. Activating Mutations at Residues 12, 13, or 61 Promote Active, GTP-Complexed ras Formation.- II. Other Activating Mutations Also Perturb the ras GDP-GTP Cycle.- G. Clinical Implications of Oncogenic ras for Diagnosis and Treatment.- I. Diagnostic and Prognostic Applications of ras Mutations.- II. Protein Prenylation: Oncogenic ras Proteins as Targets of Therapy.- H. Future Questions.- References.- 19 Dominant Inhibitory Ras Mutants: Tools for Elucidating Ras function.- A. Introduction.- B. Mechanism of Inhibitory Action.- C. Defining Biochemical Pathways Dependent upon Ras function.- D. Some Surprises Revealed by Dominant Inhibitory Ras Mutants.- E. Conclusions.- References.- 20 The Involvement of Cellular ras in Proliferative Signaling.- A. Introduction.- B. The Relationship Between Tyrosine Kinase Oncogenes and Cellular ras.- I. Neutralizing Anti-ras Antibody.- II. Inhibition in the Late G1 Phase of the Cell Cycle.- III. ras and Other Oncogene Classes.- C. A Model for Proliferative Signal Transduction.- I. Other Studies Which Support the Model.- D. Lipids and the Control of ras Activity.- I. Dependence of Lipid Mitogens upon ras.- II. Biochemical Effects of Lipids upon ras.- E. Biochemical Analyses of the Interaction Between ras and Lipids.- I. Lipids and ras-Related Proteins.- II. Neurofibromin and Lipid Inhibition.- III. Production of GAP-Inhibitory Lipids by Mitogen Stimulation.- IV. Physical Association Between GAP and Lipids.- V. Mutational Analysis of ras and the Lipid Inhibitory Phenotype.- VI. Other Studies of Lipids and GAP Activity.- VII. Tyrosine Kinases and Lipid Metabolism.- VIII. Model for the Control of Proliferation at the Level of ras Activity.- F. Cellular Factors Affecting ras Activity.- I. N17 ras Interferes with the Activation of Cellular ras.- II. RAST is Preferentially Inhibitory for Oncogenic ras.- III. Model for Inhibition of ras Activity by Dominant Inhibitory Mutants.- IV. Biochemical Support for the Idea that RAST Binds an Effector.- G. Summary.- References.- 21 Regulation of Ras-Interacting Proteins in Saccharomyces cerevisiae.- A. Introduction.- B. Regulation of Ras Activity by Guanine Nucleotides.- I. Biochemical Properties of Ras.- II. The CDC25 Gene.- III. IRA1 and IRA2 Genes.- C. Regulation of Adenylyl Cyclase by Ras.- D. Domains of Ras Interacting with Other Proteins.- E. Conclusions.- References.- 22 Lipid Modifications of Proteins in the Ras Superfamily.- A. Background.- B. Farnesylation.- I. Farnesyl-Protein Transferase.- II. Function of Farnesylation.- C. Geranylgeranylation.- D. Other Modifications.- I. Proteolysis.- II. Methylation.- III. Palmitoylation.- E. Conclusions.- References.- 23 GTPase Activating Proteins.- A. Introduction.- B. GTPase Activating Proteins for ras p21 Proteins.- I. GTPase Activating Proteins in Saccharomyces cerevisiae.- II. GTPase Activating Proteins in Schizosaccharomyces pombe.- III. GTPase Activating Proteins in Drosophila melanogaster.- IV. GTPase Activating Proteins in Mammalian Cells.- C. GTPase Activating Proteins for rap p21's.- D. GTPase Activating Proteins for rho-Like Proteins.- E. GTPase Activating Proteins for other small GTPases.- F. Concluding Remarks.- References.- 24 Guanine Nucleotide Dissociation Stimulators.- A. Introduction.- B. Possible Mechanisms for conversion to the GTP-Bound State.- C. Nonspecific Guanine Nucleotide Dissociation Stimulators.- D. Ras-Specific Guanine Nucleotide Dissociation Stimulators.- I. Mammalian Guanine Nucleotide Dissociation Stimulators.- II. Yeast Guanine Nucleotide Dissociation Stimulators: CDC25, SCD25 and ste6.- III. A Ras-Specific Guanine Nucleotide Dissociation Stimulator in Drosophila: SOS.- E. RAB3-Specific Guanine Nucleotide Dissociation Stimulator.- F. Other Guanine Nucleotide Dissociation Stimulators.- G. Conclusions.- References.- 25 The Biology of Rap.- A. Introduction.- B. Cloning/Isolation of Rap(s).- C. Posttranslational Modification of Rap Proteins.- I. Isoprenylation.- II. Phosphorylation.- D. Rap1 Regulatory Proteins.- I. GTPase Activating Proteins.- II. GDP/GTP Dissociation Stimulator.- E. Biological Activities of Rap1 Protein.- I. Antagonism of Ras by Rap1.- II. Interaction of Rap1A with the Phagocyte Reduced Nicotinamide Adenine Dinucleotide Phosphate Oxidase.- F. Conclusion.- References.- B. Vesicle Transfer/Vesicle Fusion.- 26 GTPases and Interacting Elements in Vesicle Budding and Targeting in Yeast.- A. Introduction.- B. Isolation and Characterization of Secretion Defective Yeast Strains.- C. Biochemical Analysis of Protein Transport from the Endoplasmic Reticulum to the Golgi Apparatus.- D. Sar1p Function in Vesicle Formation from the Endoplasmic Reticulum.- E. Concluding Remarks.- References.- 27 Ypt Proteins in Yeast and Their Role in Intracellular Transport.- A. Introduction.- B. Ypt Proteins in Saccharomyces derevisiae.- I. Ypt1 Protein.- II. Sec4 Protein.- III. Ypt3, Ypt6 and Ypt7 Proteins.- C. Ypt Protein Structure.- I. Nucleotide Binding.- II. Effector Region.- III. C Terminus.- D. GTPase Activating Proteins for YPT Family Members.- E. Summary.- References.- 28 Compartmentalization of rab Proteins in Mammalian Cells.- A. Subcellular Compartmentalization and Membrane Traffic.- I. Membrane Trafficking.- 1. Indications for a Role of Sec4/Ypt1/rab GTPases.- B. Localization of rab Proteins on Subcellular Compartments.- I. The rab Proteins Associated with the Biosynthetic Route.- 1. Endoplasmic Reticulum and Golgi Apparatus.- 2. The rab3a Protein on Regulated Exocytic Vesicles.- II. The rab Proteins on Endocytic Compartments.- 1. The rab5 and rab4 Proteins on Early Endosomes.- 2. The rab Proteins on Late Endocytic Compartments.- III. The Molecular Basis of rab Compartmentalization.- 1. The C-Terminal Modifications.- 2. Role of the C-Terminal Variable Region.- C. The Function of rab Proteins in Membrane Trafficking.- I. The Present Model for rab function.- II. Experimental Evidence for rab Function in Membrane Trafficking.- 1. The rab1, rab2, and rab9 Proteins are Involved in Transport Steps on the Biosynthetic Route.- 2. The rab3a Protein and Regulated Secretion.- 3. Functional Studies on rab5 and rab4.- 4. Conclusion from the Functional Data.- D. The Novel rab Proteins.- I. Why Clone More rab Sequences?.- II. Subcellular Localization.- 1. Novel Proteins on the Biosynthetic Pathway.- 2. Novel Proteins on Early Endocytic Compartments.- III. Epithelial-Specific rab Proteins?.- E. Conclusion.- References.- 29 GTPases in Transport Between Late Endosomes and the Trans Golgi Network.- A. Small GTPases in Membrane Traffic.- B. In Vitro Assays to Analyze the Role of GTP in Membrane Traffic.- I. Introduction.- II. Transport of Mannose 6-Phosphate Receptors From Late Endosomes to the trans Golgi Network In Vitro.- III. GTP?S Inhibits Endosome-to-TGN Transport In Vitro.- IV. A GTP?S-Sensitive Transport Component Requires Late Endosomes for Its Activity.- C. Role of rab Proteins in Endosome to trans Golgi Network Transport.- D. A Model for rab Protein function.- I. Recruitment of rab Proteins onto Nascent Transport Vesicles.- 1. Newly Synthesized rab Proteins are Cytosolic.- 2. Membrane Association.- II. Action of rab Proteins After Transport Vesicle Formation.- E. Future Perspectives.- References.- 30 Endocytic Function in Cell-Free System.- A. Introduction.- B. Development of Cell-Free Assays.- I. Endosomal Fusion.- II. Early Endocytic Events: Formation, Invagination, and Budding of Coated Vesicles.- III. Late Endocytic Events: Sorting, Processing, and Recycling.- C. GTPases Implicated in Endocytic Traffic.- I. Evidence Supporting a Functional Role for GTPases.- II. Rab Proteins.- III. Heterotrimeric G-Proteins.- IV. ADP-Ribosylation Factors.- D. Future Prospectives.- References.- 31 Synaptic Vesicle Membrane Traffic and the Cycle of Rab3.- A. Membrane Traffic of Synaptic Vesicles in Neurons.- B. Rab3 Proteins: Structure, Posttranslational Modifications and Subcellular Localization.- C. The Cycle of Rab3A in Nerve Terminals.- References.- 32 Regulated Exocytosis and Interorganelle Vesicular Traffic: A Comparative Analysis.- A. Introduction.- B. GTPases in Membrane Traffic: Experimental Approaches.- C. GTPases in Constitutive Transport.- I. Vesicle Formation.- II. Vesicle Targeting and Fusion.- 1. Rab Proteins.- 2. ARF Proteins.- 3. Heterotrimeric G-Proteins.- D. GTPases in Regulated Exocytosis.- I. Granule Formation.- II. Granule Targeting and Fusion.- E. Regulation of the Secretory Pathways by Transduction Systems.- I. Regulated Exocytosis.- II. Constitutive Traffic.- F. Conclusions.- References.- 33 Regulated and Constitutive Secretion Studied In Vitro: Control by GTPases at Multiple Levels.- A. Introduction.- B. The Regulated Secretory Pathway: A General Mechanism for the Control of Cell-Cell Communication and Plasma Membrane Activities.- C. Controlling Passage Through the Regulated Secretory Pathway - Distinctions Between Constitutive and Regulated Secretion.- I. Exocytosis.- II. Formation of Granules.- III. Sorting of Contents.- D. Regulation of Traffic Through the Constitutive Pathway.- E. GTPases and Intracellular Membrane Transport.- I. SAR1.- II. Trimeric G-proteins.- III. The ADP-Ribosylation Factor Family.- IV. The rab Family.- F. Conclusions.- References.- 34 The Biology of ADP-Ribosylation Factors.- A. Introduction.- B. The ARF Family of Small GTPases.- I. Structural Definition.- II. Functional Definition.- C. ARF Functions in the Yeast, Saccharomyces cerevisiae.- I. Yeast ARF Genes and Proteins.- II. Phenotypes of arf Mutants.- III. Evidence that ARF Is Required in the Secretory Pathway.- D. Biochemical Characterization of ARF Proteins.- I. ARF Purified from Mammalian Sources is Heterogeneous.- II. ARF Cofactor Activity.- III. Guanine Nucleotide Binding.- IV. GTPase Activity.- V. The Role of Myristoylation.- VI. Binding of ARF to Lipid Bilayers.- VII. Evidence that ARF is Required at Several Steps in the Secretory and Endocytic Pathways.- E. Use of ARF Antibodies.- I. Abundance of Different ARF Proteins is Quite Variable.- II. Localization of ARF Proteins in Animal Cells.- F. ARF as a Regulator of Coat Protein Binding to Membranes.- I. Brefeldin A Causes Rapid Release of ARF from Golgi Stacks.- II. An In Vitro Assay for ARF as Regulator of Coat Protein Binding.- References.- 35 Molecular Characterization of ADP-Ribosylation Factors.- A. Introduction.- B. Activation of Cholera Toxin by ADP-Ribosylation Factors.- I. Mechanism of Activation of Cholera Toxin by ADP-Ribosylation Factors.- II. Guanine Nucleotide-Dependent Association of Cholera Toxin with ADP-Ribosylation Factors.- III. Activation of Escherichia coli Heat-Labile Enterotoxin by ADP-Ribosylation Factor.- C. Structure of ADP-Ribosylation Factors.- I. Deduced Amino Acid Sequences and Gene Structure of ADP-Ribosylation Factors.- II. Expression of ADP-Ribosylation Factors in Eukaryotic Species.- D. Hormonal and Developmental Regulation of ADP-Ribosylation Factors.- E. Physiological Roles for ADP-Ribosylation Factors.- References.- C. rho and rho-Like Proteins.- 36 rho and rho-Related Proteins.- A. Introduction.- B. Sequence and Structure.- C. Expression and Localisation.- D. Upstream Regulation of rho-Like Proteins.- I. Nucleotide Exchange.- II. GTP Hydrolysis.- E. Downstream Functions of rho-Like Proteins.- I. Mammalian rho Proteins.- II. The rac Proteins.- 1. rac and the Actin Cytoskeleton.- 2. rac and the Superoxide Production.- 3. Other rho-Related Proteins.- F. Conclusions.- References.- 37 The Mammalian Homolog of the Yeast Cell-Division-Cycle Protein, CDC42: Evidence for the Involvement of a Rho-Subtype GTPase in Cell Growth Regulation.- A. Growth Factor-Coupled Signal Transduction.- B. Reconstitution of an Epidermal Growth Factor Stimulated Phosphorylation of a 22-kDa GTPase.- C. Molecular Cloning of the Human Gp/G25K Protein: Identification of this Protein as the Human Homolog of the Yeast Cell Division Cycle Protein CDC42Sc.- D. Function of CDC42Sc in Saccharomyces cerevisiae.- E. Possible Involvement of CDC42Hs in Cell Growth Regulation.- I. cDNA Transfection Studies.- II. CDC42Hs Regulatory Proteins.- 1. CDC42Hs GTPase Activating Protein.- 2. CDC42Hs Guanine Nucleotide Dissociation Stimulator.- 3. CDC42Hs Guanine Nucleotide Dissociation Inhibitor.- References.- D. Regulation of and by Small GTPases.- 38 Role of Rap1B and Its Phosphorylation in Cellular Function: A Working Model.- A. Introduction: The Rap Family of Proteins.- B. Phosphorylation of Rap1b.- I. Structural Properties.- 1. cAMP-dependent Phosphorylation of Rap1b in Human Platelets.- 2. Phosphorylation of Raplb by a Neuronal Ca2+/ Calmodulin-dependent Protein Kinase, CaM Kinase Gr.- 3. Mutational Analysis of the Protein Kinase A-dependent Phosphorylation Site of Rap1b.- 4. Phosphorylation-dependent Activation of Rap1b: Role of Guanine Nucleotide Dissociation Stimulator.- II. Physiological Properties: The Platelet Model.- 1. Thrombin-induced Association of Rap1b with Ras-GTPase Activating Protein: Effect of Phosphorylation.- 2. Ras-GAP Associates with Phospholipase C?-1 in Human Platelets.- III. A Working Model and Open Questions.- References.- 39 GDP/GTP Exchange Proteins for Small GTP-Binding Proteins.- A. Introduction.- B. Physical Properties of GDP/GTP Exchange Protein.- C. Two Actions of GDP/GTP Exchange Protein and Requirement of the Posttranslational Processing of Small GTPases for GDP/GTP Exchange Protein Actions.- D. Substrate Specificity of GDP/GTP Exchange Protein and Functional Cooperation Between Guanine Nucleotide Dissociation Stimulator and Guanine Nucleotide Dissociation Inhibitor.- E. Activation of smg p21 by Protein Kinases A and G.- F. The Function of smg Guanine Nucleotide Dissociation Stimulator in Regulating Gene Expression and Cell Poliferation.- G. The Function of smg Guanine Nucleotide Dissociation Stimulator and rho Guanine Nucleotide Dissociation Inhibitor in Regulating Superoxide Generation.- H. The Function of smg Guanine Nucleotide Dissociation Stimulator, rho, and rho Guanine Nucleotide Dissociation Inhibitor in Regulating the Actomyosin System.- I. The Function of smg p25 Guanine Nucleotide Dissociation Inhibitor in Regulating Intracellular Vesicle Transport.- J. Conclusions.- References.- 40 GTP-Mediated Communication Between Intracellular Calcium Pools.- A. Intracellular Ca2+ Signaling Pools.- I. Nature of Intracellular Ca2+ Pools.- II. Movements of Ca2+ Induced by Inositol Phosphates.- III. Intracellular Ca2+ Channels.- IV. Significance of Ca2+ Within the InsP3-Sensitive Ca2+ Pool.- B. Ca2+ Movements Activated by Guanine Nucleotides.- I. GTP-Induced Ca2+ Fluxes.- II. Ca2+ Compartments Sensitive to GTP and InsP3.- III. Distinctions Between GTP- and InsP3-Induced Ca2+ Transport.- IV. Rationale for the Action of GTP.- C. Interorganelle Translocation of Ca2+.- I. Model for GTP-Activated Ca2+ Translocation.- II. GTP-Activated Ca2+ Transfer into the InsP3-Sensitive Ca2+ Pool.- III. Isolation of InsP3-Releasable and InsP3-Recruitable Pools.- IV. Functional Organization of Ca2+-Regulatory Organelles.- D. G-Proteins and Interorganelle Transfer of Ca2+.- I. Identification of Possible G-Protein Mediators of Ca2+ Transfer.- II. Conclusions on the Role of G-Proteins.- References.- 41 Coupling of ras to the T Cell Antigen Receptor.- A. Introduction.- B. Receptors and Intracellular Signals that Regulate p21ras.- I. Activation of p21ras in Cells Other than T Lymphocytes.- II. Activation of p21ras in T Lymphocytes.- C. GTPase Activating Proteins Regulate p21ras in T Lymphocytes.- D. Mechanisms of Regulation of ras GTPase Activating Proteins in T Cells.- E. Function of p21ras in T Lymphocytes.- References.- 42 GTPases as Regulators of Regulated Secretion.- A. GTP: A Sine Qua Non for Exocytosis.- I. Ca2+-Dependent Secretion in Myeloid Granulocytes.- B. Probing Exocytosis: Permeabilised Cells.- I. GTP?S-Induced, Ca2+-Independent Exocytosis.- II. Ca2+-Induced, GTP-Dependent Exocytosis.- III. One or Two Effectors?.- 1. Chloride Suppresses and Glutamate Enhances Guanine Nucleotide Sensitivity of Exocytosis.- IV. Kinetics of Exocytosis.- 1. Mg2+ Permits Abrupt Onset.- 2. Mg2+ Deprivation Causes Onset Delays.- V. GTPases Regulate and Modulate Exocytosis in Many Cells and Tissues.- C. On the Nature of GE.- I. The Example of GS.- II. The Example of the Monomeric GTPases.- D. Single Cell Analysis of GTP?S-Induced Exocytosis.- E. Two GTPases in Regulated Exocytosis?.- References.- 43 ADP-Ribosylation of Small GTPases by Clostridium botulinum Exoenzyme C3 and Pseudomonas aeruginosa Exoenzyme S.- A. Introduction.- B. Small GTPases.- C. Clostridium botulinum Exoenzyme C3.- D. Pseudomonas aeruginosa Exoenzyme S.- E. Conclusions.- References.