bluuebunny/crossref_metadata_2025 huggingface dataset:
Computers and elections
Authors: Frenkel K. A.
Published: July 2002

Along the twists and turns of this year's presidential campaign trails, computers act as strategic tools that exert a decisive impact on capturing voters' attention. But a National Bureau of Standards study claims that system implementations are dangerously inadequate at the finish line, where carefully gleaned votes are less carefully counted.
An approach to the recursive retrieval problem in the relational database
Authors: Kuo F.-Y. , Tillquist J.
Published: July 2002

The host query language often impairs data retrieval in recursive database structures. Functional extensions to QUEL are explored in order to simplify the user interface.
Algorithm 674
Authors: Higham Nicholas J.
Published: July 2002

We omitted giving this article an ACM algorithm number when it was first published in its entirety in the December 1988 issue of
TOMS
, Vol. 14, No. 4, pp. 381–396. To correct this, we do so here, and reprint the title as a pointer to the original article.
Complexity of parallel
QR
factorization
Authors: Cosnard M. , Robert Y.
Published: July 2002

An optimal algorithm to perform the parallel QR decomposition of a dense matrix of size
N
is proposed. It is deduced that the complexity of such a decomposition is asymptotically 2
N
, when an unlimited number of processors is available.
Expert systems: perils and promise
Authors: Bobrow D. G. , Mittal S. , Stefik M. J.
Published: July 2002

Based on a review of some actual expert-system projects, guidelines are proposed for choosing appropriate applications and managing the development process.
Math proficiency
Authors: Konvalina John , Wileman Stanley A. , Stephens Larry J.
Published: July 2002

A computer science aptitude predictor was administered to students enrolled in a first technical course in computer science to determine potential for success. The study revealed significant differences in the scoring between students who withdrew from the course and those students who did not. The causes for the differences all related to the students' mathematical background: high school performance, previous computer science education, and the number of college mathematics courses taken.
A linear-time probabilistic counting algorithm for database applications
Authors: Whang Kyu-Young , Vander-Zanden Brad T. , Taylor Howard M.
Published: July 2002

We present a probabilistic algorithm for counting the number of unique values in the presence of duplicates. This algorithm has
O
(
q
) time complexity, where
q
is the number of values including duplicates, and produces an estimation with an arbitrary accuracy prespecified by the user using only a small amount of space. Traditionally, accurate counts of unique values were obtained by sorting, which has
O
(
q
log
q
) time complexity. Our technique, called
linear counting
, is based on hashing. We present a comprehensive theoretical and experimental analysis of linear counting. The analysis reveals an interesting result: A load factor (number of unique values/hash table size) much larger than 1.0 (e.g., 12) can be used for accurate estimation (e.g., 1% of error). We present this technique with two important applications to database problems: namely, (1) obtaining the column cardinality (the number of unique values in a column of a relation) and (2) obtaining the join selectivity (the number of unique values in the join column resulting from an unconditional join divided by the number of unique join column values in the relation to he joined). These two parameters are important statistics that are used in relational query optimization and physical database design.
Language Policies and Language Rights
Authors: Paulston Christina Bratt
Published: July 2002

This review is an overview of the newly developing field of language rights. It distinguishes between (a) historical/descriptive studies where language rights are treated as the resultant variable with no attempt to predict consequences, and (b) exhortatory and ideologically based studies in which language rights are considered a causal variable. An attempt at definitions follows, set within the field of language planning. Principal concerns, such as territoriality versus personality principles and individual versus collective rights, are discussed.

The review ends with an argument to consider language rights as emic rights, which is to say culture-language-context–specific rights, rather than to consider linguistic human rights from a universal rights perspective which overstates issues and masks rights to as also being rights against. We need a careful exploration of the nature of language rights and their consequences.
THE CHLOROPHYLL-CAROTENOID PROTEINS OF OXYGENIC PHOTOSYNTHESIS
Authors: Green B. R. , Durnford D. G.
Published: July 2002

▪ Abstract  The chlorophyll-carotenoid binding proteins responsible for absorption and conversion of light energy in oxygen-evolving photosynthetic organisms belong to two extended families: the Chl a binding core complexes common to cyanobacteria and all chloroplasts, and the nuclear-encoded light-harvesting antenna complexes of eukaryotic photosynthesizers (Chl a/b, Chl a/c, and Chl a proteins). There is a general consensus on polypeptide and pigment composition for higher plant pigment proteins. These are reviewed and compared with pigment proteins of chlorophyte, rhodophyte, and chromophyte algae. Major advances have been the determination of the structures of LHCII (major Chl a/b complex of higher plants), cyanobacterial Photosystem I, and the peridinen–Chl a protein of dinoflagellates to atomic resolution. Better isolation methods, improved transformation procedures, and the availability of molecular structure models are starting to provide insights into the pathways of energy transfer and the macromolecular organization of thylakoid membranes.
THE OXIDATIVE BURST IN PLANT DISEASE RESISTANCE
Authors: Lamb Chris , Dixon Richard A.
Published: July 2002

▪ Abstract  Rapid generation of superoxide and accumulation of H2O2 is a characteristic early feature of the hypersensitive response following perception of pathogen avirulence signals. Emerging data indicate that the oxidative burst reflects activation of a membrane-bound NADPH oxidase closely resembling that operating in activated neutrophils. The oxidants are not only direct protective agents, but H2O2 also functions as a substrate for oxidative cross-linking in the cell wall, as a threshold trigger for hypersensitive cell death, and as a diffusible signal for induction of cellular protectant genes in surrounding cells. Activation of the oxidative burst is a central component of a highly amplified and integrated signal system, also involving salicylic acid and perturbations of cytosolic Ca2+, which underlies the expression of disease-resistance mechanisms.
THE ETHYLENE RESPONSE PATHWAY IN ARABIDOPSIS
Authors: Kieber Joseph J.
Published: July 2002

▪ Abstract  The simple gas ethylene influences a diverse array of plant growth and developmental processes including germination, senescence, cell elongation, and fruit ripening. This review focuses on recent molecular genetic studies, principally in Arabidopsis, in which components of the ethylene response pathway have been identified. The isolation and characterization of two of these genes has revealed that ethylene sensing involves a protein kinase cascade. One of these genes encodes a protein with similarity to the ubiquitous Raf family of Ser/Thr protein kinases. A second gene shows similarity to the prokaryotic two-component histidine kinases and most likely encodes an ethylene receptor. Additional elements involved in ethylene signaling have only been identified genetically. The characterization of these genes and mutants will be discussed.
PLANT TRANSFORMATION: Problems and Strategies for Practical Application
Authors: Birch R. G.
Published: July 2002

▪ Abstract  Plant transformation is now a core research tool in plant biology and a practical tool for cultivar improvement. There are verified methods for stable introduction of novel genes into the nuclear genomes of over 120 diverse plant species. This review examines the criteria to verify plant transformation; the biological and practical requirements for transformation systems; the integration of tissue culture, gene transfer, selection, and transgene expression strategies to achieve transformation in recalcitrant species; and other constraints to plant transformation including regulatory environment, public perceptions, intellectual property, and economics. Because the costs of screening populations showing diverse genetic changes can far exceed the costs of transformation, it is important to distinguish absolute and useful transformation efficiencies. The major technical challenge facing plant transformation biology is the development of methods and constructs to produce a high proportion of plants showing predictable transgene expression without collateral genetic damage. This will require answers to a series of biological and technical questions, some of which are defined.
POLLINATION REGULATION OF FLOWER DEVELOPMENT
Authors: O'Neill Sharman D.
Published: July 2002

▪ Abstract  Pollination regulates a syndrome of developmental responses that contributes to successful sexual reproduction in higher plants. Pollination-regulated developmental events collectively prepare the flower for fertilization and embryogenesis while bringing about the loss of floral organs that have completed their function in pollen dispersal and reception. Components of this process include changes in flower pigmentation, senescence and abscission of floral organs, growth and development of the ovary, and, in certain cases, pollination also triggers ovule and female gametophyte development in anticipation of fertilization. Pollination-regulated development is initiated by the primary pollination event at the stigma surface, but because developmental processes occur in distal floral organs, the activity of interorgan signals that amplify and transmit the primary pollination signal to floral organs is implicated. Interorgan signaling and signal amplification involves the regulation of ethylene biosynthetic gene expression and interorgan transport of hormones and their precursors. The coordination of pollination- regulated flower development including gametophyte, embryo, and ovary development; pollination signaling; the molecular regulation of ethylene biosynthesis; and interorgan communication are presented.
MORE EFFICIENT PLANTS: A Consequence of Rising Atmospheric CO2?
Authors: Drake Bert G. , Gonzàlez-Meler Miquel A. , Long Steve P.
Published: July 2002

▪ Abstract  The primary effect of the response of plants to rising atmospheric CO2(Ca) is to increase resource use efficiency. Elevated Careduces stomatal conductance and transpiration and improves water use efficiency, and at the same time it stimulates higher rates of photosynthesis and increases light-use efficiency. Acclimation of photosynthesis during long-term exposure to elevated Careduces key enzymes of the photosynthetic carbon reduction cycle, and this increases nutrient use efficiency. Improved soil–water balance, increased carbon uptake in the shade, greater carbon to nitrogen ratio, and reduced nutrient quality for insect and animal grazers are all possibilities that have been observed in field studies of the effects of elevated Ca. These effects have major consequences for agriculture and native ecosystems in a world of rising atmospheric Caand climate change.
ABSCISIC ACID SIGNAL TRANSDUCTION
Authors: Leung Jeffrey , Giraudat Jérôme
Published: July 2002

▪ Abstract  The plant hormone abscisic acid (ABA) plays a major role in seed maturation and germination, as well as in adaptation to abiotic environmental stresses. ABA promotes stomatal closure by rapidly altering ion fluxes in guard cells. Other ABA actions involve modifications of gene expression, and the analysis of ABA-responsive promoters has revealed a diversity of potential cis-acting regulatory elements. The nature of the ABA receptor(s) remains unknown. In contrast, combined biophysical, genetic, and molecular approaches have led to considerable progress in the characterization of more downstream signaling elements. In particular, substantial evidence points to the importance of reversible protein phosphorylation and modifications of cytosolic calcium levels and pH as intermediates in ABA signal transduction. Exciting advances are being made in reassembling individual components into minimal ABA signaling cascades at the single-cell level.
PHOSPHATE TRANSLOCATORS IN PLASTIDS
Authors: Flügge Ulf-Ingo
Published: July 2002

▪ Abstract  During photosynthesis, energy from solar radiation is used to convert atmospheric carbon dioxide into intermediates that are used within and outside the chloroplast for a multitude of metabolic pathways. The daily fixed carbon is exported from the chloroplasts as triose phosphates and 3-phosphoglycerate. In contrast, nongreen plastids rely on the import of carbon, mainly hexose phosphates. Most organelles require the import of phosphoenolpyruvate as an immediate substrate for carbon to enter the shikimate pathway, leading to a variety of important secondary compounds. The envelope membrane of plastids contains specific translocators that are involved in these transport processes. Elucidation of the molecular structure of some of these translocators during the past few years has provided new insights in the functioning of particular translocators. This review focuses on the characterization of different classes of phosphate translocators in plastids that mediate the transport of the phosphorylated compounds in exchange with inorganic phosphate.
ENZYMES AND OTHER AGENTS THAT ENHANCE CELL WALL EXTENSIBILITY
Authors: Cosgrove Daniel J.
Published: July 2002

▪ Abstract  Polysaccharides and proteins are secreted to the inner surface of the growing cell wall, where they assemble into a network that is mechanically strong, yet remains extensible until the cells cease growth. This review focuses on the agents that directly or indirectly enhance the extensibility properties of growing walls. The properties of expansins, endoglucanases, and xyloglucan transglycosylases are reviewed and their postulated roles in modulating wall extensibility are evaluated. A summary model for wall extension is presented, in which expansin is a primary agent of wall extension, whereas endoglucanases, xyloglucan endotransglycosylase, and other enzymes that alter wall structure act secondarily to modulate expansin action.
PROBINGPLANTMETABOLISM WITHNMR
Authors: Ratcliffe R George , Shachar-Hill Yair
Published: July 2002

▪ Abstract  Analytical methods for probing plant metabolism are taking on new significance in the era of functional genomics and metabolic engineering. Among the available methods, nuclear magnetic resonance (NMR) spectroscopy is a technique that can provide insights into the integration and regulation of plant metabolism through a combination of in vivo and in vitro measurements. Thus NMR can be used to identify, quantify, and localize metabolites, to define the intracellular environment, and to explore pathways and their operation. We review these applications and their significance from a metabolic perspective. Topics of current interest include applications of NMR to metabolic flux analysis, metabolite profiling, and metabolite imaging. These and other areas are discussed in relation to NMR investigations of intermediary carbon and nitrogen metabolism. We conclude that metabolic NMR has a continuing role to play in the development of a quantitative understanding of plant metabolism and in the characterization of metabolic phenotypes.
MOLECULARBIOLOGY OFFRUITMATURATION ANDRIPENING
Authors: Giovannoni Jim
Published: July 2002

▪ Abstract  The development and maturation of fruits has received considerable scientific scrutiny because of both the uniqueness of such processes to the biology of plants and the importance of fruit as a significant component of the human diet. Molecular and genetic analysis of fruit development, and especially ripening of fleshy fruits, has resulted in significant gains in knowledge over recent years. Great strides have been made in the areas of ethylene biosynthesis and response, cell wall metabolism, and environmental factors, such as light, that impact ripening. Discoveries made in Arabidopsis in terms of general mechanisms for signal transduction, in addition to specific mechanisms of carpel development, have assisted discovery in more traditional models such as tomato. This review attempts to coalesce recent findings in the areas of fruit development and ripening.
G PROTEIN MECHANISMS: Insights from Structural Analysis
Authors: Sprang Stephen R.
Published: July 2002

This review is concerned with the structures and mechanisms of a superfamily of regulatory GTP hydrolases (G proteins). G proteins include Ras and its close homologs, translation elongation factors, and heterotrimeric G proteins. These proteins share a common structural core, exemplified by that of p21ras (Ras), and significant sequence identity, suggesting a common evolutionary origin. Three-dimensional structures of members of the G protein superfamily are considered in light of other biochemical findings about the function of these proteins. Relationships among G protein structures are discussed, and factors contributing to their low intrinsic rate of GTP hydrolysis are considered. Comparison of GTP- and GDP-bound conformations of G proteins reveals how specific contacts between the γ-phosphate of GTP and the switch II region stabilize potential effector-binding sites and how GTP hydrolysis results in collapse (or reordering) of these surfaces. A GTPase-activating protein probably binds to and stabilizes the conformation of its cognate G protein that recognizes the transition state for hydrolysis, and may insert a catalytic residue into the G protein active site. Inhibitors of nucleotide release, such as the β γ subunit of a heterotrimeric G protein, bind selectively to and stabilize the GDP-bound state. Release factors, such as the translation elongation factor, Ts, also recognize the switch regions and destabilize the Mg2+-binding site, thereby promoting GDP release. G protein–coupled receptors are expected to operate by a somewhat different mechanism, given that the GDP-bound form of many G protein α subunits does not contain bound Mg2+.
RIBONUCLEASE P: Unity and Diversity in a tRNA Processing Ribozyme
Authors: Frank Daniel N. , Pace Norman R.
Published: July 2002

Ribonuclease P (RNase P) is the endoribonuclease that generates the mature 5′-ends of tRNA by removal of the 5′-leader elements of precursor-tRNAs. This enzyme has been characterized from representatives of all three domains of life (Archaea, Bacteria, and Eucarya) ( 1 ) as well as from mitochondria and chloroplasts. The cellular and mitochondrial RNase Ps are ribonucleoproteins, whereas the most extensively studied chloroplast RNase P (from spinach) is composed solely of protein. Remarkably, the RNA subunit of bacterial RNase P is catalytically active in vitro in the absence of the protein subunit ( 2 ). Although RNA-only activity has not been demonstrated for the archaeal, eucaryal, or mitochondrial RNAs, comparative sequence analysis has established that these RNAs are homologous (of common ancestry) to bacterial RNA. RNase P holoenzymes vary greatly in organizational complexity across the phylogenetic domains, primarily because of differences in the RNase P protein subunits: Mitochondrial, archaeal, and eucaryal holoenzymes contain larger, and perhaps more numerous, protein subunits than do the bacterial holoenzymes. However, that the nonbacterial RNase P RNAs retain significant structural similarity to their catalytically active bacterial counterparts indicates that the RNA remains the catalytic center of the enzyme.
Autophagy, Cytoplasm-to-Vacuole Targeting Pathway, and Pexophagy in Yeast and Mammalian Cells
Authors: Kim John , Klionsky Daniel J.
Published: July 2002

▪ Abstract  The sequestration and delivery of cytoplasmic material to the yeast vacuole and mammalian lysosome require the dynamic mobilization of cellular membranes and specialized protein machinery. Under nutrient deprivation conditions, double-membrane vesicles form around bulk cytoplasmic cargo destined for degradation and recycling in the vacuole/lysosome. A similar process functions to remove excess organelles under vegetative conditions in which they are no longer needed. Biochemical, morphological, and molecular genetic studies in yeasts and mammalian cells have begun to elucidate the molecular details of this autophagy process. In addition, the overlap of macroautophagy with the process of pexophagy and with the biosynthetic cytoplasm-to-vacuole targeting pathway, which delivers the resident vacuolar hydrolase aminopeptidase I, indicates that these three pathways are related mechanistically. Identification and characterization of the autophagic/cytoplasm-to-vacuole protein-targeting components have revealed the essential roles for various functional classes of proteins, including a novel protein conjugation system and the machinery for vesicle formation and fusion.
Protein Splicing and Related Forms of Protein Autoprocessing
Authors: Paulus Henry
Published: July 2002

▪ Abstract  Protein splicing is a form of posttranslational processing that consists of the excision of an intervening polypeptide sequence, the intein, from a protein, accompanied by the concomitant joining of the flanking polypeptide sequences, the exteins, by a peptide bond. It requires neither cofactors nor auxiliary enzymes and involves a series of four intramolecular reactions, the first three of which occur at a single catalytic center of the intein. Protein splicing can be modulated by mutation and converted to highly specific self-cleavage and protein ligation reactions that are useful protein engineering tools. Some of the reactions characteristic of protein splicing also occur in other forms of protein autoprocessing, ranging from peptide bond cleavage to conjugation with nonprotein moieties. These mechanistic similarities may be the result of convergent evolution, but in at least one case—hedgehog protein autoprocessing—there is definitely a close evolutionary relationship to protein splicing.
Transcriptional Coactivator Complexes
Authors: Näär Anders M. , Lemon Bryan D. , Tjian Robert
Published: July 2002

▪ Abstract  The last two decades have witnessed a tremendous expansion in our knowledge of the mechanisms employed by eukaryotic cells to control gene activity. A critical insight to transcriptional control mechanisms was provided by the discovery of coactivators, a diverse array of cellular factors that connect sequence-specific DNA binding activators to the general transcriptional machinery, or that help activators and the transcriptional apparatus to navigate through the constraints of chromatin. A number of coactivators have been isolated as large multifunctional complexes, and biochemical, genetic, molecular, and cellular strategies have all contributed to uncovering many of their components, activities, and modes of action. Coactivator functions can be broadly divided into two classes: (a) adaptors that direct activator recruitment of the transcriptional apparatus, (b) chromatin-remodeling or -modifying enzymes. Strikingly, several distinct coactivator complexes nonetheless share many subunits and appear to be assembled in a modular fashion. Such structural and functional modularity could provide the cell with building blocks from which to construct a versatile array of coactivator complexes according to its needs. The extent of functional interplay between these different activities in gene-specific transcriptional regulation is only now becoming apparent, and will remain an active area of research for years to come.
Cardiac Energy Metabolism: Models of Cellular Respiration
Authors: Jafri M. Saleet , Dudycha Stephen J. , O'Rourke Brian
Published: July 2002

▪ Abstract  The heart requires a large amount of energy to sustain both ionic homeostasis and contraction. Under normal conditions, adenosine triphosphate (ATP) production meets this demand. Hence, there is a complex regulatory system that adjusts energy production to meet this demand. However, the mechanisms for this control are a topic of active debate. Energy metabolism can be divided into three main stages: substrate delivery to the tricarboxylic acid (TCA) cycle, the TCA cycle, and oxidative phosphorylation. Each of these processes has multiple control points and exerts control over the other stages. This review discusses the basic stages of energy metabolism, mechanisms of control, and the mathematical and computational models that have been used to study these mechanisms.
Structural Relationships Among Regulated and Unregulated Phosphorylases
Authors: Buchbinder Jenny L. , Rath Virginia L. , Fletterick Robert J.
Published: July 2002

▪ Abstract  Species and tissue-specific isozymes of phosphorylase display differences in regulatory properties consistent with their distinct roles in particular organisms and tissues. In this review, we compare crystallographic structures of regulated and unregulated phosphorylases, including maltodextrin phosphorylase (MalP) from Escherichia coli, glycogen phosphorylase from yeast, and mammalian isozymes from muscle and liver tissues. Mutagenesis and functional studies supplement the structural work and provide insights into the structural basis for allosteric control mechanisms. MalP, a simple, unregulated enzyme, is contrasted with the more complicated yeast and mammalian phosphorylases that have evolved regulatory sites onto the basic catalytic architecture. The human liver and muscle isozymes show differences structurally in their means of invoking allosteric activation. Phosphorylation, though common to both the yeast and mammalian enzymes, occurs at different sites and activates the enzymes by surprisingly different mechanisms.
CYCLIN-DEPENDENT KINASES: Engines, Clocks, and Microprocessors
Authors: Morgan David O.
Published: July 2002

▪ Abstract  Cyclin-dependent kinases (Cdks) play a well-established role in the regulation of the eukaryotic cell division cycle and have also been implicated in the control of gene transcription and other processes. Cdk activity is governed by a complex network of regulatory subunits and phosphorylation events whose precise effects on Cdk conformation have been revealed by recent crystallographic studies. In the cell, these regulatory mechanisms generate an interlinked series of Cdk oscillators that trigger the events of cell division.
When to Switch to Flowering
Authors: Simpson Gordon G. , Gendall Anthony R. , Dean Caroline
Published: July 2002

▪ Abstract  At a certain stage in their life cycle, plants switch from vegetative to reproductive development. This transition is regulated by multiple developmental and environmental cues. These ensure that the plant switches to flowering at a time when sufficient internal resources have been accumulated and the environmental conditions are favorable. The use of a molecular genetic approach in Arabidopsis has resulted in the identification and cloning of many of the genes involved in regulating floral transition. The current view on the molecular function of these genes, their division into different genetic pathways, and how the pathways interact in a complex regulatory network are summarized.
Adaptors for Clathrin-Mediated Traffic
Authors: Kirchhausen Tomas
Published: July 2002

▪ Abstract  Clathrin-based systems are responsible for a large portion of vesicular traffic originating from the plasma membrane and the trans-Golgi network that reaches the endosomal compartment. The assembly of cytosolic clathrin forms the scaffold required for the local deformation of the membrane and for the formation of coated pits and vesicles. In this process, clathrin interacts in a coordinated fashion with a large number of protein partners. A subset designated clathrin adaptors links integral membrane proteins to the clathrin coat, a process that results in the recruitment of specific cargo proteins to the budding vesicle. This review focuses on the most recent advances dealing with the molecular basis for sorting by clathrin adaptors.
Synaptic Vesicle Biogenesis
Authors: Hannah Matthew J. , Schmidt Anne A. , Huttner Wieland B.
Published: July 2002

▪ Abstract  Synaptic vesicles, which have been a paradigm for the fusion of a vesicle with its target membrane, also serve as a model for understanding the formation of a vesicle from its donor membrane. Synaptic vesicles, which are formed and recycled at the periphery of the neuron, contain a highly restricted set of neuronal proteins. Insight into the trafficking of synaptic vesicle proteins has come from studying not only neurons but also neuroendocrine cells, which form synaptic-like microvesicles (SLMVs). Formation and recycling of synaptic vesicles/SLMVs takes place from the early endosome and the plasma membrane. The cytoplasmic machinery of synaptic vesicle/SLMV formation and recycling has been studied by a variety of experimental approaches, in particular using cell-free systems. This has revealed distinct machineries for membrane budding and fission. Budding is mediated by clathrin and clathrin adaptors, whereas fission is mediated by dynamin and its interacting protein SH3p4, a lysophosphatidic acid acyl transferase.
Gut Feelings: Enteropathogenic E. coli (EPEC) Interactions with the Host
Authors: Goosney Danika L. , Gruenheid Samantha , Finlay B. Brett
Published: July 2002

▪ Abstract  Enteropathogenic Escherichia coli (EPEC) is a gram-negative bacterial pathogen that adheres to human intestinal epithelial cells, resulting in watery, persistent diarrhea. It subverts the host cell cytoskeleton, causing a rearrangement of cytoskeletal components into a characteristic pedestal structure underneath adherent bacteria. In contrast to other intracellular pathogens that affect the actin cytoskeleton from inside the host cytoplasm, EPEC remains extracellular and transmits signals through the host cell plasma membrane via direct injection of virulence factors by a “molecular syringe,” the bacterial type III secretion system. One injected factor is Tir, which functions as the plasma membrane receptor for EPEC adherence. Tir directly links extracellular EPEC through the epithelial membrane and firmly anchors it to the host cell actin cytoskeleton, thereby initiating pedestal formation. In addition to stimulating actin nucleation and polymerization in the host cell, EPEC activates several other signaling pathways that lead to tight junction disruption, inhibition of phagocytosis, altered ion secretion, and immune responses. This review summarizes recent developments in our understanding of EPEC pathogenesis and discusses similarities and differences between EPEC pedestals, focal contacts, and Listeria monocytogenes actin tails.
SalmonellaInteractions with Host Cells: Type III Secretion at Work
Authors: Galán Jorge E.
Published: July 2002

▪ Abstract  The bacterial pathogen Salmonella enterica has evolved a very sophisticated functional interface with its vertebrate hosts. At the center of this interface is a specialized organelle, the type III secretion system, that directs the translocation of bacterial proteins into the host cell. Salmonella spp. encode two such systems that deliver a remarkable array of bacterial proteins capable of modulating a variety of cellular functions, including actin cytoskeleton dynamics, nuclear responses, and endocytic trafficking. Many of these bacterial proteins operate by faithful mimicry of host proteins, in some cases representing the result of extensive molecular tinkering and convergent evolution. The coordinated action of these type III secreted proteins secures the replication and survival of the bacteria avoiding overt damage to the host. The study of this remarkable pathogen is not only illuminating general paradigms in microbial pathogenesis but is also providing valuable insight into host cell functions.
Getting the Message Across: The Intracellular Localization of mRNAs in Higher Eukaryotes
Authors: Palacios Isabel M. , Johnston Daniel St.
Published: July 2002

▪ Abstract  The intracellular localization of mRNA, a common mechanism for targeting proteins to specific regions of the cell, probably occurs in most if not all polarized cell types. Many of the best characterized localized mRNAs are found in oocytes and early embryos, where they function as localized determinants that control axis formation and the development of the germline. However, mRNA localization has also been shown to play an important role in somatic cells, such as neurons, where it may be involved in learning and memory. mRNAs can be localized by a variety of mechanisms including local protection from degradation, diffusion to a localized anchor, and active transport, and we consider the evidence for each of these processes, before discussing the cis-acting elements that direct the localization of specific mRNAs and the trans-acting factors that bind them.
The Carbon Budget in Soils
Authors: Amundson Ronald
Published: July 2002

▪ Abstract  The global soil C reservoir, ∼1500 Gt of C (1 Gt = 1012kg of C), is dynamic on decadal time scales and is sensitive to climate and human disturbance. At present, as a result of land use, soil C is a source of atmospheric CO2in the tropics and possibly part of a sink in northern latitudes. Here I review the processes responsible for maintaining the global soil C reservoir and what is known about how it responds to direct and indirect human perturbations.

“I am fire and air; my other elements I give to baser life”

     —William Shakespeare, Antony and Cleopatra
Mantle Mixing: The Generation, Preservation, and Destruction of Chemical Heterogeneity
Authors: van Keken Peter E. , Hauri Erik H. , Ballentine Chris J.
Published: July 2002

▪ Abstract  Observations of the geochemical diversity of mid-oceanic ridge and ocean-island basalts have traditionally been attributed to the existence of large-scale mantle heterogeneity. In particular, the layered convection model has provided an important conceptual basis for discussing the chemical evolution of the Earth. In this model, a long-term boundary is assumed between a well-mixed and depleted upper mantle and a heterogeneous and more primitive lower mantle. The existence of high3He/4He in ocean-island sources has been used to argue for the preservation of a primitive component in the deep mantle. Nevertheless, a primitive deep layer is difficult to reconcile with the abundant lithophile isotopic evidence for recycling of oceanic crust and the lack of preservation of primitive mantle. In addition, the widespread acceptance of geophysical evidence for whole mantle flow has made straightforward application of the layered convection model problematic. Model calculations show that whole mantle convection with present day heat flow and surface velocities is sufficiently vigorous to mix large-scale heterogeneity to an extent that is incompatible with the geochemical observations. Several concepts have been proposed in recent years to resolve the apparent conflicts between the various observational constraints and theoretical interpretations. The suggestions include the presence of deeper layering, preservation of highly viscous blobs, core mantle interaction, and strong temporal variations in mantle dynamics. Although these models generally appear to solve parts of the puzzle, at present no single model is able to account for all of the major observations. The reconciliation of conflicting evidence awaits improvements in observational and experimental techniques integrated with better model testing of hypotheses for the generation and destruction of mantle heterogeneity.
POSSIBLE LARGEST-SCALE TRENDS IN ORGANISMAL EVOLUTION: Eight “Live Hypotheses”
Authors: McShea Daniel W.
Published: July 2002

▪ Abstract  Historically, a great many features of organisms have been said to show a trend over the history of life, and many rationales for such trends have been proposed. Here I review eight candidates, eight “live hypotheses” that are inspiring research on largest-scale trends today: entropy, energy intensiveness, evolutionary versatility, developmental depth, structural depth, adaptedness, size, and complexity. For each, the review covers the principal arguments that have been advanced for why a trend is expected, as well as some of the empirical approaches that have been adopted. Also discussed are three conceptual matters arising in connection with trend studies: 1. Alternative bases for classifying trends: pattern versus dynamics; 2. alternative modes in which largest-scale trends have been studied: “exploratory” versus “skeptical”; and 3. evolutionary progress.
Polymorphism in Systematics and Comparative Biology
Authors: Wiens John J.
Published: July 2002

▪ Abstract  Polymorphism, or variation within species, is common in all kinds of data and is the major focus of research on microevolution. However, polymorphism is often ignored by those who study macroevolution: systematists and comparative evolutionary biologists. Polymorphism may have a profound impact on phylogeny reconstruction, species-delimitation, and studies of character evolution. A variety of methods are used to deal with polymorphism in phylogeny reconstruction, and many of these methods have been extremely controversial for more than 20 years. Recent research has attempted to address the accuracy of these methods (their ability to estimate the true phylogeny) and to resolve these issues, using computer simulation, congruence, and statistical analyses. These studies suggest three things: that (a) the exclusion of polymorphic characters (as is commonly done in morphological phylogenetics) is unjustified and may greatly decrease accuracy relative to analyses that include these characters; (b) methods that incorporate frequency information on polymorphic characters tend to perform best, and (c) distance and likelihood methods designed for polymorphic data may often outperform parsimony methods. Although rarely discussed, polymorphism may also have a major impact on comparative studies of character evolution, such as the reconstruction of ancestral character states. Finally, polymorphism is an important issue in the delimitation of species, although this area has been somewhat neglected methodologically. The integration of within-species variation and microevolutionary processes into studies of systematics and comparative evolutionary biology is another example of the benefits of exchange of ideas between the fields of population genetics and systematics.
GEOTHERMAL ENERGY FROM THE EARTH: Its Potential Impact as an Environmentally Sustainable Resource
Authors: Mock John E. , Tester Jefferson W. , Wright P. Michael
Published: July 2002

▪ Abstract  Geothermal energy technology is reviewed in terms of its current impact and future potential as an energy source. In general, the geothermal energy resource base is large and well distributed globally. Geothermal systems have a number of positive social characteristics (they are simple, safe, and adaptable systems with modular 1–50 MW [thermal (t) or electric (e)] plants capable of providing continuous baseload, load following, or peaking capacity) and benign environmental attributes (negligible emissions of CO2, SOx, NOx, and particulates, and modest land and water use). Because these features are compatible with sustainable growth of global energy supplies in both developed and developing countries, geothermal energy is an attractive option to replace fossil and fissile fuels. In 1997, about 7,000 MWe of base-load generating capacity and over 15,000 MWt of heating capacity from high-grade geothermal resources are in commercial use worldwide. A key question is whether these levels can grow to a point where geothermal energy is more universally available and thus have a significant impact on global energy supplies in the twenty-first century. Such an achievement will require the economic development of low-grade resources.

The current status of commercial and emerging technologies for electric power production and direct heat use is reviewed for the major geothermal resources including hydrothermal, geopressured, hot dry rock, and magma. Typically, high-temperature resources (>150°C) provide base-load generating capacity while lower-temperature resources provide energy for geothermally assisted heat pumps and for direct use in domestic, agricultural, and aquacultural heating applications. Critical development issues relating to resource quality and distribution, drilling costs, and reservoir productivity are discussed in the context of their economic impact on production costs. Advanced drilling and improved heat mining methods are suggested as approaches to increase the worldwide use of geothermal energy by reducing field development costs. With these improvements, lower-grade resources can compete in growing global energy markets that are currently controlled by abundant and low-cost fossil fuels.
Queries on the Human Use of the Earth
Authors: Kates Robert W.
Published: July 2002

[Figure: see text]

▪ Abstract  The central question of my scientific work has been, what is and ought to be the human use of the earth? It has been pursued collectively, with mentor, colleagues, students, and friends as a set of research questions related to hazards, hunger, and sustainable development. Regarding hazard, I tried to understand why people persist in occupying areas subject to natural and technological hazards and how adaptation made this possible. An extended stay in Africa to research both environment and development led to new queries. Why does hunger persist amid a world of plenty, and what can be done to end it? Can there be a transition to sustainability that over the next two generations would meet human needs and reduce hunger and poverty while maintaining the essential life support systems of the planet? All three themes and the research methods used to pursue them come together in an emerging sustainability science.
BEHAVIOR AND ECOLOGICAL GENETICS OF WIND-BORNE MIGRATION BY INSECTS
Authors: Gatehouse A. G.
Published: July 2002

▪ Abstract  Wind-borne migration, in which migrants ascend to altitudes at which they are transported downwind, has evolved independently in several insect orders. The use of a range of observational techniques, including ground and air-borne radars, has provided new insights into how the migrants' behavior can influence the distance traveled and the degree of dispersal during migration. Simultaneously in recent years, advances in our knowledge of the genetics of migratory potential have provided a basis for understanding how the stochastic effects of the winds on destinations and the pattern of habitat distribution in space and time maintain variation in these traits in populations of wind-borne migrants. This variation, in turn, is an essential factor in the ability of these insects, many of which are important pests, to track often unpredictable changes in the spatial distribution of suitable habitats.
MALARIA PARASITE DEVELOPMENT IN MOSQUITOES
Authors: Beier John C.
Published: July 2002

▪ Abstract  Mosquitoes of the genus Anopheles transmit malaria parasites to humans. Anopheles mosquito species vary in their vector potential because of environmental conditions and factors affecting their abundance, blood-feeding behavior, survival, and ability to support malaria parasite development. In the complex life cycle of the parasite in female mosquitoes, a process termed sporogony, mosquitoes acquire gametocyte-stage parasites from blood-feeding on an infected host. The parasites carry out fertilization in the midgut, transform to ookinetes, then oocysts, which produce sporozoites. Sporozoites invade the salivary glands and are transmitted when the mosquito feeds on another host. Most individual mosquitoes that ingest gametocytes do not support development to the sporozoite stage. Bottlenecks occur at every stage of the cycle in the mosquito. Powerful new techniques and approaches exist for evaluating malaria parasite development and for identifying mechanisms regulating malaria parasite–vector interactions. This review focuses on those interactions that are important for the development of new approaches for evaluating and blocking transmission in nature.
EMERGING AND RESURGING VECTOR-BORNE DISEASES
Authors: Gratz Norman G.
Published: July 2002

▪ Abstract  Over the last four decades, a number of arthropod-borne infections have been recognized for the first time. Some have become of considerable public health importance, such as dengue hemorrhagic fever (DHF), and others are spreading geographically and their incidence is increasing. There has been an important recrudescence of several long-known vector-borne diseases. Malaria, leishmaniasis, dengue, and plague have resurged in numerous foci, in some cases where they were thought to be under effective control. In most instances, the appearance of new diseases and syndromes and the resurgence of old can be associated with ecological changes that have favored increased vector densities. Dam construction, irrigation and other development projects, urbanization, and deforestation have all resulted in changes in vector population densities that appear to have enabled the emergence of new diseases and the resurgence of old diseases. Greatly increased human travel has spread infectious agents, introducing them into areas in which they had been hitherto absent. It is essential to understand the factors that caused increased vector densities and hence the transmission of disease to prevent the emergence and resurgence of more diseases, as well as to serve as a basis for effective control.
THE EVOLUTION AND DEVELOPMENT OF DIPTERAN WING VEINS: A Systematic Approach
Authors: Stark Julian , Bonacum James , Remsen James , DeSalle Rob
Published: July 2002

▪ Abstract  In this review, we use the wing veins of dipteran insects as potential models for understanding the evolution of development. We briefly discuss previous work in this field and examine the genetic complexity of wing formation, discussing the genes involved in wing formation and their roles in Drosophila wing development and vein formation. Furthermore, patterns of wing vein formation, addition, and reduction are discussed as they occur throughout the Diptera. Using the phyletic phenocopy paradigm, we draw attention to many wing vein morphologies that phenocopy various wing mutants in Drosophila melanogaster. The systematic issues of the nature of characters, homology, and the role of modern developmental approaches to evolutionary studies, which has recently become important, can be addressed from the perspective of the wing. We argue that further developmental evolutionary studies, and the interpretation of data therefrom, must be conducted within the context of a well-supported phylogeny of the organisms under study.
Molecular Mechanism and Cellular Distribution of Insect Circadian Clocks
Authors: Giebultowicz Jadwiga M.
Published: July 2002

▪ Abstract  Circadian clocks are endogenous timing mechanisms that control molecular, cellular, physiological, and behavioral rhythms in all organisms from unicellulars to humans. Circadian rhythms influence many aspects of insect biology, finetuning life functions to the light and temperature cycles associated with the solar day. Genetic studies in the fruit fly Drosophila melanogaster have led to the cloning and characterization of several genes involved in the mechanism of the circadian clock. Periodic transcription and translation of these clock genes form the basis of a molecular feedback loop that has a “circa” 24-hour period. Rhythmic expression of clock genes in specific brain neurons appears to control behavioral rhythms in adult flies. However, clock genes are also expressed in other tissues, both within and outside of the nervous system. These observations prompted chronobiologists to investigate whether nonneural tissues possess intrinsic circadian clocks, what role they may be playing, and what the relationships are between clocks in the nervous system and those in peripheral tissues. Answers to those questions are providing important insights into the overall organization of the circadian system in insects.