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D Lancet

Publications and source records attributed to D Lancet.

At least 37 records · Page 2Linked to original sources
PubMed2000

The genomic structure of human olfactory receptor genes.

The genomic and cDNA structures were studied for eight human olfactory receptor (OR) genes within the chromosome 17p13.3 cluster. A common gene structure was revealed, which included an approximately 1-kb intronless coding region terminated by a signal for polyadenylation and a variable number of upstream noncoding exons. The latter were found to be alternatively spliced, giving rise to different isoforms of OR mRNA. While the initial exons mostly agreed with previous computer predictions and were conserved within OR subfamilies, other upstream exons were novel and idiosyncratic. In some cases, repetitive sequences were involved in the generation of splice sites and putative transcription control elements. Such gene structure is consistent with early repertoire enhancement by retrogene generation, which was likely followed by extensive genomic duplication. Each OR gene had a unique signature of transcription factor elements, consistent with a combinatorial expression control mechanism.

Alternative Splicing↗
PubMed2000

Compositional genomes: prebiotic information transfer in mutually catalytic noncovalent assemblies.

Mutually catalytic sets of simple organic molecules have been suggested to be capable of self-replication and rudimentary chemical evolution. Previous models for the behavior of such sets have analyzed the global properties of short biopolymer ensembles by using graph theory and a mean field approach. In parallel, experimental studies with the autocatalytic formation of amphiphilic assemblies (e.g., lipid vesicles or micelles) demonstrated self-replication properties resembling those of living cells. Combining these approaches, we analyze here the kinetic behavior of small heterogeneous assemblies of spontaneously aggregating molecules, of the type that could form readily under prebiotic conditions. A statistical formalism for mutual rate enhancement is used to numerically simulate the detailed chemical kinetics within such assemblies. We demonstrate that a straightforward set of assumptions about kinetically enhanced recruitment of simple amphiphilic molecules, as well as about the spontaneous growth and splitting of assemblies, results in a complex population behavior. The assemblies manifest a significant degree of homeostasis, resembling the previously predicted quasi-stationary states of biopolymer ensembles (Dyson, F. J. (1982) J. Mol. Evol. 18, 344-350). Such emergent catalysis-driven, compositionally biased entities may be viewed as having rudimentary "compositional genomes." Our analysis addresses the question of how mutually catalytic metabolic networks, devoid of sequence-based biopolymers, could exhibit transfer of chemical information and might undergo selection and evolution. This computed behavior may constitute a demonstration of natural selection in populations of molecules without genetic apparatus, suggesting a pathway from random molecular assemblies to a minimal protocell.

Catalysis↗
PubMed2000

Sequence, structure, and evolution of a complete human olfactory receptor gene cluster.

The olfactory receptor (OR) gene cluster on human chromosome 17p13.3 was subjected to mixed shotgun automated DNA sequencing. The resulting 412 kb of genomic sequence include 17 OR coding regions, 6 of which are pseudogenes. Six of the coding regions were discovered only upon genomic sequencing, while the others were previously reported as partial sequences. A comparison of DNA sequences in the vicinity of the OR coding regions revealed a common gene structure with an intronless coding region and at least one upstream noncoding exon. Potential gene control regions including specific pyrimidine:purine tracts and Olf-1 sites have been identified. One of the pseudogenes apparently has evolved into a CpG island. Four extensive CpG islands can be discerned within the cluster, not coupled to specific OR genes. The cluster is flanked at its telomeric end by an unidentified open reading frame (C17orf2) with no significant similarity to any known protein. A high proportion of the cluster sequence (about 60%) belongs to various families of interspersed repetitive elements, with a clear predominance of LINE repeats. The OR genes in the cluster belong to two families and seven subfamilies, which show a relatively high degree of intermixing along the cluster, in seemingly random orientations. This genomic organization may be best accounted for by a complex series of evolutionary events.

Base Sequence↗
PubMed2000

The olfactory receptor gene superfamily: data mining, classification, and nomenclature.

The vertebrate olfactory receptor (OR) subgenome harbors the largest known gene family, which has been expanded by the need to provide recognition capacity for millions of potential odorants. We implemented an automated procedure to identify all OR coding regions from published sequences. This led us to the identification of 831 OR coding regions (including pseudogenes) from 24 vertebrate species. The resulting dataset was subjected to neighbor-joining phylogenetic analysis and classified into 32 distinct families, 14 of which include only genes from tetrapodan species (Class II ORs). We also report here the first identification of OR sequences from a marsupial (koala) and a monotreme (platypus). Analysis of these OR sequences suggests that the ancestral mammal had a small OR repertoire, which expanded independently in all three mammalian subclasses. Classification of "fish-like" (Class I) ORs indicates that some of these ancient ORs were maintained and even expanded in mammals. A nomenclature system for the OR gene superfamily is proposed, based on a divergence evolutionary model. The nomenclature consists of the root symbol 'OR', followed by a family numeral, subfamily letter(s), and a numeral representing the individual gene within the subfamily. For example, OR3A1 is an OR gene of family 3, subfamily A, and OR7E12P is an OR pseudogene of family 7, subfamily E. The symbol is to be preceded by a species indicator. We have assigned the proposed nomenclature symbols for all 330 human OR genes in the database. A WWW tool for automated name assignment is provided.

Animals↗
PubMed2000

Identification of the gene causing mucolipidosis type IV.

Mucolipidosis type IV (MLIV) is an autosomal recessive, neurodegenerative, lysosomal storage disorder characterized by psychomotor retardation and ophthalmological abnormalities including corneal opacities, retinal degeneration and strabismus. Most patients reach a maximal developmental level of 12?15 months. The disease was classified as a mucolipidosis following observations by electron microscopy indicating the lysosomal storage of lipids together with water-soluble, granulated substances. Over 80% of the MLIV patients diagnosed are Ashkenazi Jews, including severely affected and mildly affected patients. The gene causing MLIV was previously mapped to human chromosome 19p13.2-13.3 in a region of approximately 1 cM (ref. 7). Haplotype analysis in the MLIV gene region of over 70 MLIV Ashkenazi chromosomes indicated the existence of two founder chromosomes among 95% of the Ashkenazi MLIV families: a major haplotype in 72% and a minor haplotype in 23% of the MLIV chromosomes (ref. 7, and G.B., unpublished data). The remaining 5% are distinct haplotypes found only in single patients. The basic metabolic defect causing the lysosomal storage in MLIV has not yet been identified. Thus, positional cloning was an alternative to identify the MLIV gene. We report here the identification of a new gene in this human chromosomal region in which MLIV-specific mutations were identified.

Amino Acid Sequence↗
PubMed2000

Dichotomy of single-nucleotide polymorphism haplotypes in olfactory receptor genes and pseudogenes.

Substantial efforts are focused on identifying single-nucleotide polymorphisms (SNPs) throughout the human genome, particularly in coding regions (cSNPs), for both linkage disequilibrium and association studies. Less attention, however, has been directed to the clarification of evolutionary processes that are responsible for the variability in nucleotide diversity among different regions of the genome. We report here the population sequence diversity of genomic segments within a 450-kb cluster of olfactory receptor (OR) genes on human chromosome 17. We found a dichotomy in the pattern of nucleotide diversity between OR pseudogenes and introns on the one hand and the closely interspersed intact genes on the other. We suggest that weak positive selection is responsible for the observed patterns of genetic variation. This is inferred from a lower ratio of polymorphism to divergence in genes compared with pseudogenes or introns, high non-synonymous substitution rates in OR genes, and a small but significant overall reduction in variability in the entire OR gene cluster compared with other genomic regions. The dichotomy among functionally different segments within a short genomic distance requires high recombination rates within this OR cluster. Our work demonstrates the impact of weak positive selection on human nucleotide diversity, and has implications for the evolution of the olfactory repertoire.

Alleles↗
PubMed2000

GESTALT: a workbench for automatic integration and visualization of large-scale genomic sequence analyses.

SUMMARY: The GESTALT Workbench is a WWW-based tool for genomic sequence analysis, comparison and annotation, with strong emphasis on visualization. GESTALT integrates graphically the output of diverse sequence analysis algorithms producing an information-rich, interactive genomic map. AVAILABILITY: The GESTALT Workbench, as well as a more detailed description, are available at http://bioinfo. weizmann.ac.il/GESTALT/.

Algorithms↗
PubMed2000

Composing life.

Textbooks often assert that life began with specialized complex molecules, such as RNA, that are capable of making their own copies. This scenario has serious difficulties, but an alternative has remained elusive. Recent research and computer simulations have suggested that the first steps toward life may not have involved biopolymers. Rather, non-covalent protocellular assemblies, generated by catalyzed recruitment of diverse amphiphilic and hydrophobic compounds, could have constituted the first systems capable of information storage, inheritance and selection. A complex chain of evolutionary events, yet to be deciphered, could then have led to the common ancestors of today's free-living cells, and to the appearance of DNA, RNA and protein enzymes.

Biological Evolution↗
PubMed2000

Harvesting the human genome: the Israeli perspective.

The post-genome era is at our door, and soon the complete human genome sequence will be available for the next set of goals. Israel is well equipped and skilled to join the worldwide harvest of the human genome, but additional massive government investment is required. This will affect various domains of activity, including the fields of diagnostics and therapeutics. The technologies and know-how described above constitute the basis for future human genome applications in Israel.

Computational Biology↗
PubMed1999

kPROT: a knowledge-based scale for the propensity of residue orientation in transmembrane segments. Application to membrane protein structure prediction.

Modeling of integral membrane proteins and the prediction of their functional sites requires the identification of transmembrane (TM) segments and the determination of their angular orientations. Hydrophobicity scales predict accurately the location of TM helices, but are less accurate in computing angular disposition. Estimating lipid-exposure propensities of the residues from statistics of solved membrane protein structures has the disadvantage of relying on relatively few proteins. As an alternative, we propose here a scale of knowledge-based Propensities for Residue Orientation in Transmembrane segments (kPROT), derived from the analysis of more than 5000 non-redundant protein sequences. We assume that residues that tend to be exposed to the membrane are more frequent in TM segments of single-span proteins, while residues that prefer to be buried in the transmembrane bundle interior are present mainly in multi-span TMs. The kPROT value for each residue is thus defined as the logarithm of the ratio of its proportions in single and multiple TM spans. The scale is refined further by defining it for three discrete sections of the TM segment; namely, extracellular, central, and intracellular. The capacity of the kPROT scale to predict angular helical orientation was compared to that of alternative methods in a benchmark test, using a diversity of multi-span alpha-helical transmembrane proteins with a solved 3D structure. kPROT yielded an average angular error of 41 degrees, significantly lower than that of alternative scales (62 degrees -68 degrees ). The new scale thus provides a useful general tool for modeling and prediction of functional residues in membrane proteins. A WWW server (http://bioinfo.weizmann.ac.il/kPROT) is available for automatic helix orientation prediction with kPROT.

Amino Acid Sequence↗
PubMed1999

Primate evolution of an olfactory receptor cluster: diversification by gene conversion and recent emergence of pseudogenes.

The olfactory receptor (OR) subgenome harbors the largest known gene family in mammals, disposed in clusters on numerous chromosomes. We have carried out a comparative evolutionary analysis of the best characterized genomic OR gene cluster, on human chromosome 17p13. Fifteen orthologs from chimpanzee (localized to chromosome 19p15), as well as key OR counterparts from other primates, have been identified and sequenced. Comparison among orthologs and paralogs revealed a multiplicity of gene conversion events, which occurred exclusively within OR subfamilies. These appear to lead to segment shuffling in the odorant binding site, an evolutionary process reminiscent of somatic combinatorial diversification in the immune system. We also demonstrate that the functional mammalian OR repertoire has undergone a rapid decline in the past 10 million years: while for the common ancestor of all great apes an intact OR cluster is inferred, in present-day humans and great apes the cluster includes nearly 40% pseudogenes.

Animals↗
PubMed1999

The variable and conserved interfaces of modeled olfactory receptor proteins.

The accumulation of hundreds of olfactory receptor (OR) sequences, along with the recent availability of detailed models of other G-protein-coupled receptors, allows us to analyze the OR amino acid variability patterns in a structural context. A Fourier analysis of 197 multiply aligned olfactory receptor sequences showed an alpha-helical periodicity in the variability profile. This was particularly pronounced in the more variable transmembranal segments 3, 4, and 5. Rhodopsin-based homology modeling demonstrated that the inferred variable helical faces largely point to the interior of the receptor barrel. We propose that a set of 17 hypervariable residues, which point to the barrel interior and are more extracellularly disposed, constitute the odorant complementarity determining regions. While 12 of these residues coincide with established ligand-binding contact positions in other G-protein-coupled receptors, the rest are suggested to form an olfactory-unique aspect of the binding pocket. Highly conserved olfactory receptor-specific sequence motifs, found in the second and third intracellular loops, may comprise the G-protein recognition epitope. The prediction of olfactory receptor functional sites provides concrete suggestions of site-directed mutagenesis experiments for altering ligand and G-protein specificity.

Amino Acid Sequence↗
PubMed1998

Genome dynamics, evolution, and protein modeling in the olfactory receptor gene superfamily.

The human olfactory subgenome represents several hundred olfactory receptor (OR) genes in a dozen or more clusters on several chromosomes. One OR gene cluster on human chromosome 17 has been characterized by us in detail. Based on a large-scale DNA sequence analysis, we have identified events of gene duplication and fusion as well as the generation of pseudogenes. The latter instances of 'gene death' could underlie the widespread phenomenon of human specific anosmias. Sixteen OR coding regions were found on this cluster, and six of them are pseudogenes. One of these pseudogenes, OR17-23, was found to be an intact open reading frame in an old world monkey. This may be a reflection of an OR repertoire diminution in man. A homology model of the OR protein was constructed by utilizing the rich information available on approximately 200 OR sequences. The putative odorant complementarity determining regions (CDR) was found to consist of 20 hypervariable residues facing an interior caving defined by transmembrane helices 3, 4 and 5. Such a model could be useful in analyzing additional OR gene sequences in the human genome in terms of odorant binding.

Base Sequence↗
PubMed1998

Organization and evolution of olfactory receptor genes on human chromosome 11.

Olfactory receptors (OR) are encoded by a large multigene family including hundreds of members dispersed throughout the human genome. Cloning and mapping studies have determined that a large proportion of the olfactory receptor genes are located on human chromosomes 6, 11, and 17, as well as distributed on other chromosomes. In this paper, we describe and characterize the organization of olfactory receptor genes on human chromosome 11 by using degenerate PCR-based probes to screen chromosome 11-specific and whole genome clone libraries for members of the OR gene family. OR genes were identified by DNA sequencing and then localized to regions of chromosome 11. Physical maps of several gene clusters were constructed to determine the chromosomal relationships between various members of the family. This work identified 25 new OR genes located on chromosome 11 in at least seven distinct regions. Three of these regions contain gene clusters that include additional members of this gene family not yet identified by sequencing. Phylogenetic analysis of the newly described OR genes suggests a mechanism for the generation of genetic diversity.

Amino Acid Sequence↗
PubMed1998

Molecular biology of olfactory receptors.

OR proteins bind odorant ligands and transmit a G-protein-mediated intracellular signal, resulting in generation of an action potential. The accumulation of DNA sequences of hundreds of OR genes provides an opportunity to predict features related to their structure, function and evolutionary diversification. The OR repertoire has evolved a variable ligand-binding site that ascertains recognition of multiple odorants, coupled to constant regions that mediate the cAMP-mediated signal transduction. The cellular second messenger underlies the responses to diverse odorants through the direct gating of olfactory-specific cation channels. This situation necessitates a mechanism of cellular exclusion, whereby each sensory neuron expresses only one receptor type, which in turn influences axonal projections. A 'synaptic image' of the OR repertoire thus encodes the detected odorant in the central nervous system.

Animals↗
PubMed1998

GeneCards: a novel functional genomics compendium with automated data mining and query reformulation support.

MOTIVATION: Modern biology is shifting from the 'one gene one postdoc' approach to genomic analyses that include the simultaneous monitoring of thousands of genes. The importance of efficient access to concise and integrated biomedical information to support data analysis and decision making is therefore increasing rapidly, in both academic and industrial research. However, knowledge discovery in the widely scattered resources relevant for biomedical research is often a cumbersome and non-trivial task, one that requires a significant amount of training and effort. RESULTS: To develop a model for a new type of topic-specific overview resource that provides efficient access to distributed information, we designed a database called 'GeneCards'. It is a freely accessible Web resource that offers one hypertext 'card' for each of the more than 7000 human genes that currently have an approved gene symbol published by the HUGO/GDB nomenclature committee. The presented information aims at giving immediate insight into current knowledge about the respective gene, including a focus on its functions in health and disease. It is compiled by Perl scripts that automatically extract relevant information from several databases, including SWISS-PROT, OMIM, Genatlas and GDB. Analyses of the interactions of users with the Web interface of GeneCards triggered development of easy-to-scan displays optimized for human browsing. Also, we developed algorithms that offer 'ready-to-click' query reformulation support, to facilitate information retrieval and exploration. Many of the long-term users turn to GeneCards to quickly access information about the function of very large sets of genes, for example in the realm of large-scale expression studies using 'DNA chip' technology or two-dimensional protein electrophoresis. AVAILABILITY: Freely available at http://bioinformatics.weizmann.ac.il/cards/ CONTACT: cards@bioinformatics.weizmann.ac.il

Algorithms↗
PubMed1998

Graded Autocatalysis Replication Domain (GARD): kinetic analysis of self-replication in mutually catalytic sets.

A Graded Autocatalysis Replication Domain (GARD) model is proposed, which provides a rigorous kinetic analysis of simple chemical sets that manifest mutual catalysis. It is shown that catalytic closure can sustain self replication up to a critical dilution rate, lambda c, related to the graded extent of mutual catalysis. We explore the behavior of vesicles containing GARD species whose mutual catalysis is governed by a previously published statistical distribution. In the population thus generated, some GARD vesicles display a significantly higher replication efficiency than most others. GARD thus represents a simple model for primordial chemical selection of mutually catalytic sets.

Catalysis↗