Proteins and Functions of the Endoplasmic Reticulum The Contribution of Systematic Approaches to Characterizing the

Schekman Lazar Dimitrov, Sheung Kwan Lam and Randy Protein Folding in the Endoplasmic Reticulum Ineke Braakman and Daniel N. Hebert Reticulum and Beyond Sphingolipid Homeostasis in the Endoplasmic David K. Breslow Interconnections with Other Organelles Endoplasmic Reticulum Structure and Amber R. English and Gia K. Voeltz Endoplasmic Reticulum Characterizing the Proteins and Functions of the The Contribution of Systematic Approaches to

[1]  D. Breslow,et al.  Sphingolipid homeostasis in the endoplasmic reticulum and beyond. , 2013, Cold Spring Harbor perspectives in biology.

[2]  Franco J. Vizeacoumar,et al.  Interaction landscape of membrane-protein complexes in Saccharomyces cerevisiae , 2012, Nature.

[3]  Adam Frost,et al.  Functional Repurposing Revealed by Comparing S. pombe and S. cerevisiae Genetic Interactions , 2012, Cell.

[4]  David Y. Thomas,et al.  An Interaction Map of Endoplasmic Reticulum Chaperones and Foldases* , 2012, Molecular & Cellular Proteomics.

[5]  S. Munro,et al.  A Systematic Approach to Pair Secretory Cargo Receptors with Their Cargo Suggests a Mechanism for Cargo Selection by Erv14 , 2012, PLoS biology.

[6]  M. A. Surma,et al.  Flexibility of a Eukaryotic Lipidome – Insights from Yeast Lipidomics , 2012, PloS one.

[7]  Albert Pineda Rodó,et al.  In Vivo Determination of Organellar pH Using a Universal Wavelength-Based Confocal Microscopy Approach , 2012, PloS one.

[8]  Zhuchu Chen,et al.  Proteomic and Bioinformatics Analyses of Mouse Liver Microsomes , 2012, International Journal of Proteomics.

[9]  S. Henry,et al.  Metabolism and Regulation of Glycerolipids in the Yeast Saccharomyces cerevisiae , 2012, Genetics.

[10]  I. Tabas,et al.  Role of endoplasmic reticulum stress in metabolic disease and other disorders. , 2012, Annual review of medicine.

[11]  Nicholas T. Ingolia,et al.  High-Resolution View of the Yeast Meiotic Program Revealed by Ribosome Profiling , 2011, Science.

[12]  Kazuhiro Nagata,et al.  Protein folding and quality control in the ER. , 2012, Cold Spring Harbor perspectives in biology.

[13]  P. Walter,et al.  The Unfolded Protein Response: From Stress Pathway to Homeostatic Regulation , 2011, Science.

[14]  J. Weissman,et al.  Road to Ruin: Targeting Proteins for Degradation in the Endoplasmic Reticulum , 2011, Science.

[15]  Maya Schuldiner,et al.  Getting the whole picture: combining throughput with content in microscopy , 2011, Journal of Cell Science.

[16]  M. Schuldiner,et al.  Staying in touch: the molecular era of organelle contact sites. , 2011, Trends in biochemical sciences.

[17]  Julian Mintseris,et al.  A Protein Complex Network of Drosophila melanogaster , 2011, Cell.

[18]  Giovanni Gadda,et al.  Design and application of a class of sensors to monitor Ca2+ dynamics in high Ca2+ concentration cellular compartments , 2011, Proceedings of the National Academy of Sciences.

[19]  D. Moore,et al.  Endoplasmic reticulum stress and glucose homeostasis , 2011, Current opinion in clinical nutrition and metabolic care.

[20]  I. Braakman,et al.  Protein folding and modification in the mammalian endoplasmic reticulum. , 2011, Annual review of biochemistry.

[21]  A. Palmer,et al.  Measuring steady-state and dynamic endoplasmic reticulum and Golgi Zn2+ with genetically encoded sensors , 2011, Proceedings of the National Academy of Sciences.

[22]  Wolfgang Huber,et al.  Mapping of signaling networks through synthetic genetic interaction analysis by RNAi , 2011, Nature Methods.

[23]  Frederick S. Vizeacoumar,et al.  Systematic exploration of essential yeast gene function with temperature-sensitive mutants , 2011, Nature Biotechnology.

[24]  D. Ron,et al.  Integrating the mechanisms of apoptosis induced by endoplasmic reticulum stress , 2011, Nature Cell Biology.

[25]  D. Muddiman,et al.  N-linked global glycan profiling by nanoLC mass spectrometry. , 2011, Methods in molecular biology.

[26]  M. Schuldiner,et al.  Advanced methods for high-throughput microscopy screening of genetically modified yeast libraries. , 2011, Methods in molecular biology.

[27]  E. Lundberg,et al.  Towards a knowledge-based Human Protein Atlas , 2010, Nature Biotechnology.

[28]  P. Bork,et al.  A systematic screen for protein–lipid interactions in Saccharomyces cerevisiae , 2010, Molecular systems biology.

[29]  J. Weissman,et al.  Membranes in balance: mechanisms of sphingolipid homeostasis. , 2010, Molecular cell.

[30]  Chih-yuan Chiang,et al.  A Human MAP Kinase Interactome , 2010, Nature Methods.

[31]  Ron Shamir,et al.  A plasma-membrane E-MAP reveals links of the eisosome with sphingolipid metabolism and endosomal trafficking , 2010, Nature Structural &Molecular Biology.

[32]  Dongsup Kim,et al.  Analysis of a genome-wide set of gene deletions in the fission yeast Schizosaccharomyces pombe , 2010, Nature Biotechnology.

[33]  E. Sammels,et al.  Intracellular Ca2+ storage in health and disease: a dynamic equilibrium. , 2010, Cell calcium.

[34]  Gary D Bader,et al.  The Genetic Landscape of a Cell , 2010, Science.

[35]  Christer S. Ejsing,et al.  Orm family proteins mediate sphingolipid homeostasis , 2010, Nature.

[36]  S. Carmi,et al.  Persistent ER Stress Induces the Spliced Leader RNA Silencing Pathway (SLS), Leading to Programmed Cell Death in Trypanosoma brucei , 2010, PLoS pathogens.

[37]  Y. Hannun,et al.  An overview of sphingolipid metabolism: from synthesis to breakdown. , 2010, Advances in experimental medicine and biology.

[38]  K. Mori,et al.  Signalling pathways in the unfolded protein response: development from yeast to mammals. , 2009, Journal of biochemistry.

[39]  Maya Schuldiner,et al.  Explorations in topology-delving underneath the surface of genetic interaction maps. , 2009, Molecular bioSystems.

[40]  S. Subramaniam,et al.  Application of Proteomic Marker Ensembles to Subcellular Organelle Identification* , 2009, Molecular & Cellular Proteomics.

[41]  Peter Walter,et al.  Supporting Online Material for An ER-Mitochondria Tethering Complex Revealed by a Synthetic Biology Screen , 2009 .

[42]  R. Zahedi,et al.  Analysis of the membrane proteome of canine pancreatic rough microsomes identifies a novel Hsp40, termed ERj7 , 2009, Proteomics.

[43]  Silvere Pagant,et al.  Genomewide Analysis Reveals Novel Pathways Affecting Endoplasmic Reticulum Homeostasis, Protein Modification and Quality Control , 2009, Genetics.

[44]  A. Fortunato.  Quantitative high-throughput analysis of synthetic genetic interactions in Caenorhabditis elegans by RNA interference , 2009, Genomics.

[45]  R. Loewith,et al.  Functional interactions between sphingolipids and sterols in biological membranes regulating cell physiology. , 2009, Molecular biology of the cell.

[46]  D. Rotin,et al.  High-content Functional Screen to Identify Proteins that Correct F508del-CFTR Function*S , 2009, Molecular & Cellular Proteomics.

[47]  P. Fagone,et al.  Membrane phospholipid synthesis and endoplasmic reticulum function This work was supported by National Institutes of Health Grant GM-45737, by Cancer Center Support Grant CA21765, and by the American Lebanese Syrian Associated Charities. Published, JLR Papers in Press, October 23, 2008. , 2009, Journal of Lipid Research.

[48]  S. Collins,et al.  Comprehensive Characterization of Genes Required for Protein Folding in the Endoplasmic Reticulum , 2009, Science.

[49]  Christer S. Ejsing,et al.  Global analysis of the yeast lipidome by quantitative shotgun mass spectrometry , 2009, Proceedings of the National Academy of Sciences.

[50]  Y. Hiraoka,et al.  Localization of gene products using a chromosomally tagged GFP‐fusion library in the fission yeast Schizosaccharomyces pombe , 2009, Genes to cells : devoted to molecular & cellular mechanisms.

[51]  M. Bäckström,et al.  High-throughput and high-sensitivity nano-LC/MS and MS/MS for O-glycan profiling. , 2009, Methods in molecular biology.

[52]  A. Trusina,et al.  Real-Time Redox Measurements during Endoplasmic Reticulum Stress Reveal Interlinked Protein Folding Functions , 2008, Cell.

[53]  A. Barabasi,et al.  High-Quality Binary Protein Interaction Map of the Yeast Interactome Network , 2008, Science.

[54]  Sean R. Collins,et al.  A tool-kit for high-throughput, quantitative analyses of genetic interactions in E. coli , 2008, Nature Methods.

[55]  Blanche Schwappach,et al.  The GET Complex Mediates Insertion of Tail-Anchored Proteins into the ER Membrane , 2008, Cell.

[56]  Huiming Ding,et al.  eSGA: E. coli synthetic genetic array analysis , 2008, Nature Methods.

[57]  Sean R. Collins,et al.  A comprehensive strategy enabling high-resolution functional analysis of the yeast genome , 2008, Nature Methods.

[58]  A. Merrill,et al.  Biodiversity of sphingoid bases ("sphingosines") and related amino alcohols. , 2008, Journal of lipid research.

[59]  Randal J. Kaufman,et al.  From endoplasmic-reticulum stress to the inflammatory response , 2008, Nature.

[60]  C. Landry,et al.  An in Vivo Map of the Yeast Protein Interactome , 2008, Science.

[61]  Karl Mechtler,et al.  BAC TransgeneOmics: a high-throughput method for exploration of protein function in mammals , 2008, Nature Methods.

[62]  Robert P. St.Onge,et al.  The Chemical Genomic Portrait of Yeast: Uncovering a Phenotype for All Genes , 2008, Science.

[63]  Y. Jigami,et al.  Lipid remodeling of GPI-anchored proteins and its function. , 2008, Biochimica et biophysica acta.

[64]  P. Koulen,et al.  Proteomic analysis of mouse brain microsomes: identification and bioinformatic characterization of endoplasmic reticulum proteins in the mammalian central nervous system. , 2008, Journal of proteome research.

[65]  P. Walter,et al.  Endoplasmic reticulum stress in disease pathogenesis. , 2008, Annual review of pathology.

[66]  Barry P. Young,et al.  Inheritance of cortical ER in yeast is required for normal septin organization , 2007, The Journal of cell biology.

[67]  Joshua M. Stuart,et al.  A global analysis of genetic interactions in Caenorhabditis elegans , 2007, Journal of biology.

[68]  Nevan J Krogan,et al.  High-throughput genetic interaction mapping in the fission yeast Schizosaccharomyces pombe , 2007, Nature Methods.

[69]  J. Weissman,et al.  A Molecular Caliper Mechanism for Determining Very Long-Chain Fatty Acid Length , 2007, Cell.

[70]  R. Sitia,et al.  Managing and exploiting stress in the antibody factory , 2007, FEBS letters.

[71]  J. Michalski,et al.  Analysis of protein glycosylation by mass spectrometry , 2007, Nature Protocols.

[72]  Karin Lanthaler,et al.  Genomic analysis of the secretion stress response in the enzyme-producing cell factory Aspergillus niger , 2007, BMC Genomics.

[73]  Jef D Boeke,et al.  dSLAM analysis of genome-wide genetic interactions in Saccharomyces cerevisiae. , 2007, Methods.

[74]  Christian A. Grove,et al.  Insight into transcription factor gene duplication from Caenorhabditis elegans Promoterome-driven expression patterns , 2007, BMC Genomics.

[75]  Erich E. Wanker,et al.  UniHI: an entry gate to the human protein interactome , 2006, Nucleic Acids Res..

[76]  Robert E. Kearney,et al.  Quantitative Proteomics Analysis of the Secretory Pathway , 2006, Cell.

[77]  P. Novick,et al.  Ptc1p regulates cortical ER inheritance via Slt2p , 2006, The EMBO journal.

[78]  Martin T. Wells,et al.  Multiple Endoplasmic Reticulum-to-Nucleus Signaling Pathways Coordinate Phospholipid Metabolism with Gene Expression by Distinct Mechanisms* , 2006, Journal of Biological Chemistry.

[79]  S. Henry,et al.  Inositol Induces a Profound Alteration in the Pattern and Rate of Synthesis and Turnover of Membrane Lipids in Saccharomyces cerevisiae* , 2006, Journal of Biological Chemistry.

[80]  A. Fraser,et al.  Systematic mapping of genetic interactions in Caenorhabditis elegans identifies common modifiers of diverse signaling pathways , 2006, Nature Genetics.

[81]  G. von Heijne,et al.  A global topology map of the Saccharomyces cerevisiae membrane proteome. , 2006, Proceedings of the National Academy of Sciences of the United States of America.

[82]  Y. Hiraoka,et al.  ORFeome cloning and global analysis of protein localization in the fission yeast Schizosaccharomyces pombe , 2006, Nature Biotechnology.

[83]  R. Westerberg,et al.  Fatty acid elongases in mammals: their regulation and roles in metabolism. , 2006, Progress in lipid research.

[84]  Xiaohui S. Xie,et al.  A Mammalian Organelle Map by Protein Correlation Profiling , 2006, Cell.

[85]  Sean R. Collins,et al.  Global landscape of protein complexes in the yeast Saccharomyces cerevisiae , 2006, Nature.

[86]  P. Silver,et al.  Genomic association of the proteasome demonstrates overlapping gene regulatory activity with transcription factor substrates. , 2006, Molecular cell.

[87]  K. N. Chandrika,et al.  Analysis of the human protein interactome and comparison with yeast, worm and fly interaction datasets , 2006, Nature Genetics.

[88]  H. Mori,et al.  Construction of Escherichia coli K-12 in-frame, single-gene knockout mutants: the Keio collection , 2006, Molecular systems biology.

[89]  N. Perrimon,et al.  Functional genomics reveals genes involved in protein secretion and Golgi organization , 2006, Nature.

[90]  Joseph L. Goldstein,et al.  Protein Sensors for Membrane Sterols , 2006, Cell.

[91]  M. Bard,et al.  Cloning of the late genes in the ergosterol biosynthetic pathway ofSaccharomyces cerevisiae—A review , 1995, Lipids.

[92]  W. Bowen,et al.  Decay of Endoplasmic Reticulum-Localized mRNAs During the Unfolded Protein Response , 2006 .

[93]  A. Tong,et al.  Synthetic genetic array analysis in Saccharomyces cerevisiae. , 2006, Methods in molecular biology.

[94]  Sean R. Collins,et al.  A strategy for extracting and analyzing large-scale quantitative epistatic interaction data , 2006, Genome Biology.

[95]  Sean R. Collins,et al.  Exploration of the Function and Organization of the Yeast Early Secretory Pathway through an Epistatic Miniarray Profile , 2005, Cell.

[96]  Kenjiro Sakaki,et al.  Genetic Interactions Due to Constitutive and Inducible Gene Regulation Mediated by the Unfolded Protein Response in C. elegans , 2005, PLoS genetics.

[97]  Michael Gribskov,et al.  Characterization of the yeast ionome: a genome-wide analysis of nutrient mineral and trace element homeostasis in Saccharomyces cerevisiae , 2005, Genome Biology.

[98]  W. Lennarz,et al.  Studies of yeast oligosaccharyl transferase subunits using the split-ubiquitin system: topological features and in vivo interactions. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[99]  Martin T. Wells,et al.  Genome-wide Analysis Reveals Inositol, Not Choline, as the Major Effector of Ino2p-Ino4p and Unfolded Protein Response Target Gene Expression in Yeast* , 2005, Journal of Biological Chemistry.

[100]  P. Novick,et al.  Ice2p is important for the distribution and structure of the cortical ER network in Saccharomyces cerevisiae , 2005, Journal of Cell Science.

[101]  Chi-Huey Wong,et al.  Printed covalent glycan array for ligand profiling of diverse glycan binding proteins. , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[102]  B. Wouters,et al.  Activating Transcription Factor 4 Is Translationally Regulated by Hypoxic Stress , 2004, Molecular and Cellular Biology.

[103]  T. Hughes,et al.  Exploration of Essential Gene Functions via Titratable Promoter Alleles , 2004, Cell.

[104]  P. Novick,et al.  Dynamics and inheritance of the endoplasmic reticulum , 2004, Journal of Cell Science.

[105]  Christopher J. R. Loewen,et al.  Phospholipid Metabolism Regulated by a Transcription Factor Sensing Phosphatidic Acid , 2004, Science.

[106]  David Botstein,et al.  Diverse and specific gene expression responses to stresses in cultured human cells. , 2004, Molecular biology of the cell.

[107]  Michael T. Hallett,et al.  The Hera database and its use in the characterization of endoplasmic reticulum proteins , 2004, Bioinform..

[108]  Gary D Bader,et al.  Global Mapping of the Yeast Genetic Interaction Network , 2004, Science.

[109]  S. L. Wong,et al.  A Map of the Interactome Network of the Metazoan C. elegans , 2004, Science.

[110]  R. Sriburi,et al.  Stressed-out B cells? Plasma-cell differentiation and the unfolded protein response. , 2004, Trends in immunology.

[111]  James R. Knight,et al.  A Protein Interaction Map of Drosophila melanogaster , 2003, Science.

[112]  L. Glimcher,et al.  XBP-1 Regulates a Subset of Endoplasmic Reticulum Resident Chaperone Genes in the Unfolded Protein Response , 2003, Molecular and Cellular Biology.

[113]  E. O’Shea,et al.  Global analysis of protein localization in budding yeast , 2003, Nature.

[114]  Choukri Ben Mamoun,et al.  Genome Expression Analysis in Yeast Reveals Novel Transcriptional Regulation by Inositol and Choline and New Regulatory Functions for Opi1p, Ino2p, and Ino4p* , 2003, Journal of Biological Chemistry.

[115]  Jay D. Horton,et al.  Combined analysis of oligonucleotide microarray data from transgenic and knockout mice identifies direct SREBP target genes , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[116]  R. Kamath,et al.  Genome-wide RNAi screening in Caenorhabditis elegans. , 2003, Methods.

[117]  A. Barberis,et al.  Cell growth selection system to detect extracellular and transmembrane protein interactions. , 2003, Biochimica et biophysica acta.

[118]  Ari Helenius,et al.  Quality control in the endoplasmic reticulum , 2003, Nature Reviews Molecular Cell Biology.

[119]  Hiderou Yoshida,et al.  A time-dependent phase shift in the mammalian unfolded protein response. , 2003, Developmental cell.

[120]  M. Chrispeels,et al.  Genomic Analysis of the Unfolded Protein Response in Arabidopsis Shows Its Connection to Important Cellular Processes Online version contains Web-only data. Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.007609. , 2003, The Plant Cell Online.

[121]  G. Daum,et al.  Triacylglycerol biosynthesis in yeast , 2003, Applied Microbiology and Biotechnology.

[122]  J. Vance.  Molecular and cell biology of phosphatidylserine and phosphatidylethanolamine metabolism. , 2003, Progress in nucleic acid research and molecular biology.

[123]  K. Mori,et al.  Distinct roles of activating transcription factor 6 (ATF6) and double-stranded RNA-activated protein kinase-like endoplasmic reticulum kinase (PERK) in transcription during the mammalian unfolded protein response. , 2002, The Biochemical journal.

[124]  Ronald W. Davis,et al.  Functional profiling of the Saccharomyces cerevisiae genome , 2002, Nature.

[125]  Gary D Bader,et al.  Systematic identification of protein complexes in Saccharomyces cerevisiae by mass spectrometry , 2002, Nature.

[126]  P. Bork,et al.  Functional organization of the yeast proteome by systematic analysis of protein complexes , 2002, Nature.

[127]  Gary D Bader,et al.  Systematic Genetic Analysis with Ordered Arrays of Yeast Deletion Mutants , 2001, Science.

[128]  P. Novick,et al.  Aux1p/Swa2p is required for cortical endoplasmic reticulum inheritance in Saccharomyces cerevisiae. , 2001, Molecular biology of the cell.

[129]  R. Ozawa,et al.  A comprehensive two-hybrid analysis to explore the yeast protein interactome , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[130]  S. Jentsch,et al.  Activation of a Membrane-Bound Transcription Factor by Regulated Ubiquitin/Proteasome-Dependent Processing , 2000, Cell.

[131]  Peter Walter,et al.  Functional and Genomic Analyses Reveal an Essential Coordination between the Unfolded Protein Response and ER-Associated Degradation , 2000, Cell.

[132]  P. Brown,et al.  Degradation of proteins from the ER of S. cerevisiae requires an intact unfolded protein response pathway. , 2000, Molecular cell.

[133]  Gero Miesenböck,et al.  Visualizing secretion and synaptic transmission with pH-sensitive green fluorescent proteins , 1998, Nature.

[134]  R. Tsien,et al.  green fluorescent protein , 2020, Catalysis from A to Z.

[135]  H. Zinszner,et al.  Identification of novel stress‐induced genes downstream of chop , 1998, The EMBO journal.

[136]  I. Stagljar,et al.  A genetic system based on split-ubiquitin for the analysis of interactions between membrane proteins in vivo. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[137]  H. Mewes,et al.  Overview of the yeast genome. , 1997, Nature.

[138]  J. Rine,et al.  Role of 26S proteasome and HRD genes in the degradation of 3-hydroxy-3-methylglutaryl-CoA reductase, an integral endoplasmic reticulum membrane protein. , 1996, Molecular biology of the cell.

[139]  J. Fassler,et al.  Temperature-sensitive Yeast GPI Anchoring Mutants gpi2 and gpi3 Are Defective in the Synthesis of N-Acetylglucosaminyl Phosphatidylinositol. , 1995, The Journal of Biological Chemistry.

[140]  P. Orlean,et al.  Isolation and characterization of yeast glycosylphosphatidylinositol anchoring mutants. , 1995, Methods in enzymology.

[141]  J. Rothman,et al.  Mechanisms of intracellular protein transport , 1994, Nature.

[142]  R. Schekman,et al.  COPII: A membrane coat formed by Sec proteins that drive vesicle budding from the endoplasmic reticulum , 1994, Cell.

[143]  P. Ross-Macdonald,et al.  Large-scale analysis of gene expression, protein localization, and gene disruption in Saccharomyces cerevisiae. , 1994, Genes & development.

[144]  O. Ozier-Kalogeropoulos,et al.  A simple and efficient method for direct gene deletion in Saccharomyces cerevisiae. , 1993, Nucleic acids research.

[145]  Teizo Fujita,et al.  Deficiency of the GPI anchor caused by a somatic mutation of the PIG-A gene in paroxysmal nocturnal hemoglobinuria , 1993, Cell.

[146]  T. Kinoshita,et al.  Cloning of a human gene, PIG-F, a component of glycosylphosphatidylinositol anchor biosynthesis, by a novel expression cloning strategy. , 1993, The Journal of biological chemistry.

[147]  Paul Tempst,et al.  SNAP receptors implicated in vesicle targeting and fusion , 1993, Nature.

[148]  T. Miyata,et al.  The cloning of PIG-A, a component in the early step of GPI-anchor biosynthesis. , 1993, Science.

[149]  J. Rothman,et al.  Molecular dissection of the secretory pathway , 1992, Nature.

[150]  R. Schekman,et al.  A yeast mutant defective at an early stage in import of secretory protein precursors into the endoplasmic reticulum , 1987, The Journal of cell biology.

[151]  P. Robbins,et al.  Temperature-sensitive yeast mutants deficient in asparagine-linked glycosylation. , 1982, The Journal of biological chemistry.

[152]  R. Schekman,et al.  Order of events in the yeast secretory pathway , 1981, Cell.

[153]  R. Schekman,et al.  Identification of 23 complementation groups required for post-translational events in the yeast secretory pathway , 1980, Cell.

[154]  R. Schekman,et al.  Secretion and cell-surface growth are blocked in a temperature-sensitive mutant of Saccharomyces cerevisiae , 1979, Proceedings of the National Academy of Sciences.