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At least 523 records · Page 29Linked to original sources

PubMed2005

Molecular genetics of mosquito resistance to malaria parasites.

Malaria parasites are transmitted by the bite of an infected mosquito, but even efficient vector species possess multiple mechanisms that together destroy most of the parasites present in an infection. Variation between individual mosquitoes has allowed genetic analysis and mapping of loci controlling several resistance traits, and the underlying mechanisms of mosquito response to infection are being described using genomic tools such as transcriptional and proteomic analysis. Malaria infection imposes fitness costs on the vector, but various forms of resistance inflict their own costs, likely leading to an evolutionary tradeoff between infection and resistance. Plasmodium development can be successfully completed onlyin compatible mosquito-parasite species combinations, and resistance also appears to have parasite specificity. Studies of Drosophila, where genetic variation in immunocompetence is pervasive in wild populations, offer a comparative context for understanding coevolution of the mosquito-malaria relationship. More broadly, plants also possess systems of pathogen resistance with features that are structurally conserved in animal innate immunity, including insects, and genomic datasets now permit useful comparisons of resistance models even between such diverse organisms.

Animals↗

PubMed1994

Diversity within diversity: molecular approaches to studying microbial interactions with insects.

DNA sequence information has greatly augmented the number of characters available for analysis in phylogenetic research. Nowhere is this more evident than in studies of microbial evolution. Ribosomal DNA sequence data has simultaneously permitted the distinction between individual species and the inference of their phylogenetic relationships in many cases where both were formerly impossible. These have contributed to our understanding of the ecology of particular microbe-host interactions and the history of these relationships over evolutionary time. We describe examples from two ends of the ecological spectrum in insect/bacterial associations: one in which bacteria mediate host cytoplasmic incompatibility and parthenogenesis, and the other in which mycetocyte bacteria augment host nutrition. In the former, the pattern of bacterial interaction is general, with the same or closely related strains of the genus Wolbachia associating with a wide range of insect taxa. In the latter, concordance between host and microbe phylogenies suggests cospeciation between bacteria and host, although it is as yet unclear whether this process has involved step-wise, reciprocal coevolution. We conclude with a discussion of how developments in molecular techniques may aid in analyzing more complex interactions between insects and microbes.

Animals↗

PubMed2003

Cell surface receptors for gammaretroviruses.

Evidence obtained during the last few years has greatly extended our understanding of the cell surface receptors that mediate infections of retroviruses and has provided many surprising insights. In contrast to other cell surface components such as lectins or proteoglycans that influence infections indirectly by enhancing virus adsorption onto specific cells, the true receptors induce conformational changes in the viral envelope glycoproteins that are essential for infection. One surprise is that all of the cell surface receptors for gamma-retroviruses are proteins that have multiple transmembrane (TM) sequences, compatible with their identification in known instances as transporters for important solutes. In striking contrast, almost all other animal viruses use receptors that exclusively have single TM sequences, with the sole proven exception we know of being the coreceptors used by lentiviruses. This evidence strongly suggests that virus genera have been prevented because of their previous evolutionary adaptations from switching their specificities between single-TM and multi-TM receptors. This evidence also implies that gamma-retroviruses formed by divergent evolution from a common origin millions of years ago and that individual viruses have occasionally jumped between species (zoonoses) while retaining their commitment to using the orthologous receptor of the new host. Another surprise is that many gamma-retroviruses use not just one receptor but pairs of closely related receptors as alternatives. This appears to have enhanced viral survival by severely limiting the likelihood of host escape mutations. All of the receptors used by gamma-retroviruses contain hypervariable regions that are often heavily glycosylated and that control the viral host range properties, consistent with the idea that these sequences are battlegrounds of virus-host coevolution. However, in contrast to previous assumptions, we propose that gamma-retroviruses have become adapted to recognize conserved sites that are important for the receptor's natural function and that the hypervariable sequences have been elaborated by the hosts as defense bulwarks that surround the conserved viral attachment sites. Previously, it was believed that binding to receptors directly triggers a series of conformational changes in the viral envelope glycoproteins that culminate in fusion of the viral and cellular membranes. However, new evidence suggests that gamma-retroviral association with receptors triggers an obligatory interaction or cross-talk between envelope glycoproteins on the viral surface. If this intermediate step is prevented, infection fails. Conversely, in several circumstances this cross-talk can be induced in the absence of a cell surface receptor for the virus, in which case infection can proceed efficiently. This new evidence strongly implies that the role of cell surface receptors in infections of gamma-retroviruses (and perhaps of other enveloped animal viruses) is more complex and interesting than was previously imagined. Recently, another gammaretroviral receptor with multiple transmembrane sequences was cloned. See Prassolov, Y., Zhang, D., Ivanov, D., Lohler, J., Ross, S.R., and Stocking, C. Sodium-dependent myo-inositol transporter 1 is a receptor for Mus cervicolor M813 murine leukemia virus.

Animals↗

PubMed2002

The HCMV gene products US2 and US11 target MHC class I molecules for degradation in the cytosol.

Over millions of years of coevolution with their hosts, viruses have developed highly effective strategies to elude the host immune system. The degradation of major histocompatibility complex (MHC) class I heavy chains by human cytomegalovirus (HCMV) is an example of this. Two HCMV proteins, US2 and US11, target newly synthesized MHC class I heavy chains for destruction via a pathway that involves ubiquitin-dependent retrograde transport, or "dislocation", of the heavy chains from the ER to the cytosol, where the proteins are degraded by proteasomes. In this review, US2- and US11-mediated degradation of MHC class I heavy chains is discussed in relation to data concerning the degradation of other ER luminal proteins. A new, unified model for translocon-facilitated dislocation and degradation of MHC class I heavy chains is presented.

Cytomegalovirus↗

PubMed1991

Classification of cell receptors.

This manuscript constitutes a first attempt to categorize the cell receptors. Based on evolutionary and biological characteristics, it is possible to classify ligand-receptor units into original families. Certain dynamic patterns that could not be classified previously lead us towards the ligand-receptor unit. Biological information is transformed at the receptor by cellular transduction and effector pathways. The dynamic code is compared with the genetic code. The dynamic code controls the biological information patterns necessary for the integral function and structure of cells, tissue, organs, and organisms. The genetic code controls the assembly and molecular structure of proteins. The original families can be assigned certain original functions. A coevolution of ligand-receptor and dynamic code is revealed. For the time being the most useful approach to receptor classification would seem to be based on the organization of the molecular and protein structure of receptors. Two classes of receptor can be described: receptors for cyclic hydrophobic compounds and membrane receptors. Until we know of the families of single membrane-spanning receptors, fourfold membrane-spanning receptors, sevenfold membrane-spanning receptors, fourfold membrane-spanning receptors. For the sevenfold membrane-spanning receptor the identity of conformation and dynamics of biological function has been established. Light and peptide ligands are used as examples. A systems theory for information transduction at receptors is introduced which can also describe the processes of sensitivity modulation.

Amino Acid Sequence↗

PubMed1992

Epizootics of Salmonella infection in poultry may be the result of modern selective breeding practices.

This paper discusses the hypothesis that a major factor in the epizootics of Salmonella infection in poultry is a declining host genetic diversity. A computer model is described which is based on models that have been previously used to investigate host-pathogen coevolution in cereal crops. It is shown that, as host genetic diversity declines, parasite diversity also declines to a lower equilibrium level. With a highly diverse host, parasite numbers decline to zero. With a homogeneous host population, after an initial decline, there is a rapid increase in parasite numbers, due to the selection of a particularly well adapted parasite strain. This simple computer simulation is used as the basis for a discussion of the literature supporting the suggestion that a major factor in the epizootic of Salmonella in poultry is related to the low genetic diversity of commercial poultry flocks.

Animals↗

PubMed1995

The contribution of DNA slippage to eukaryotic nuclear 18S rRNA evolution.

Six of 204 eukaryotic nuclear small-subunit ribosomal RNA sequences analyzed show a highly significant degree of clustering of short sequence motifs that indicates the fixation of products of replication slippage within them in their recent evolutionary history. A further 72 sequences show weaker indications of sequence repetition. Repetitive sequences in SSU rRNAs are preferentially located in variable regions and in particular in V4 and V7. The conserved region immediately 5' to V7 (C7) is also consistently repetitive. Whereas variable regions vary in length and appear to have evolved by the fixation of slippage products, C7 shows no indication of length variation. Repetition within C7 is therefore either not a consequence of slippage or reflects very ancient slippage events. The phylogenetic distribution of sequence simplicity in small-subunit rRNAs is patchy, being largely confined to the Mammalia, Apicomplexa, Tetrahymenidae, and Trypanosomatidae. The regions of the molecule associated with sequence simplicity vary with taxonomic grouping as do the sequence motifs undergoing slippage. Comparison of rates of insertion and substitution in a lineage within the genus Plasmodium confirms that both rates are higher in variable regions than in conserved regions. The insertion rate in variable regions is substantially lower than the substitution rate, suggesting that selection acts more strongly on slippage products than on point mutations in these regions. Patterns of coevolution between variable regions may reflect the consequences of selection acting on the incorporation of slippage-derived sequences across the gene.

Animals↗

PubMed1992

On the evolution of the bacterial major sigma factors.

The existence of internal sequence homologies between the N-terminal halves of the gram-negative bacterial major sigma factors and their C-terminal halves, which correspond to minor factors, is reported. In the case of Escherichia-Salmonella sigma-70, an apparent homology was even found between the C-terminal helix-turn-helix DNA-binding motif and the corresponding region of the peptide N half, which, however, is not directly engaged in promoter recognition. It is proposed that major sigma factors may have originated by duplication and fusion of a DNA unit related to the ancestral gene for the whole sigma family. Coevolution of major sigma structures and complex promoters is suggested.

Amino Acid Sequence↗

PubMed1995

Structure, function and evolution of seryl-tRNA synthetases: implications for the evolution of aminoacyl-tRNA synthetases and the genetic code.

Two aspects of the evolution of aminoacyl-tRNA synthetases are discussed. Firstly, using recent crystal structure information on seryl-tRNA synthetase and its substrate complexes, the coevolution of the mode of recognition between seryl-tRNA synthetase and tRNA(ser) in different organisms is reviewed. Secondly, using sequence alignments and phylogenetic trees, the early evolution of class 2 aminoacyl-tRNA synthetases is traced. Arguments are presented to suggest that synthetases are not the oldest of protein enzymes, but survived as RNA enzymes during the early period of the evolution of protein catalysts. In this view, the relatedness of the current synthetases, as evidenced by the division into two classes with their associated subclasses, reflects the replacement of RNA synthetases by protein synthetases. This process would have been triggered by the acquisition of tRNA 3' end charging activity by early proteins capable of activating small molecules (e.g., amino acids) with ATP. If these arguments are correct, the genetic code was essentially frozen before the protein synthetases that we know today came into existence.

Acylation↗

PubMed1995

Molecular evolution of transfer RNA from two precursor hairpins: implications for the origin of protein synthesis.

In this paper we are going to present a model for the coevolution of major components of the protein synthesis machinery in a primordial RNA world. We propose that the essential prerequisites for RNA-based protein synthesis, i.e., tRNA-like molecules, ribozymic charging catalysts, small-subunit(SSU) rRNA, and large-subunit(LSU) rRNA, evolved from the same ancestral RNA molecule. Several arguments are considered which suggest that tRNA-like molecules were derived by tandem joining of template-flanking hairpin structures involved in replication control. It is further argued that the ancestors of contemporary group I tRNA introns catalyzed such hairpin joining reactions, themselves also giving rise to the ribosomal RNAs. Our model includes a general stereochemical principle for the interaction between ribozymes and hairpin-derived recognition structures, which can be applied to such seemingly different processes as RNA polymerization, aminoacylation, tRNA decoding, and peptidyl transfer, implicating a common origin for these fundamental functions. These and other considerations suggest that generation and evolution of tRNA were coupled to the evolution of synthetases, ribosomal RNAs, and introns from the beginning and have been a consequence arising from the original function of tRNA precursor hairpins as replication and recombination control elements.

Animals↗

PubMed1993

The paradox of MHC-DRB exon/intron evolution: alpha-helix and beta-sheet encoding regions diverge while hypervariable intronic simple repeats coevolve with beta-sheet codons.

Twenty-one different caprine and 13 ovine MHC-DRB exon 2 sequences were determined including part of the adjacent introns containing simple repetitive (gt)n(ga)m elements. The positions for highly polymorphic DRB amino acids vary slightly among ungulates and other mammals. From man and mouse to ungulates the basic (gt)n(ga)m structure is fixed in evolution for 7 x 10(7) years whereas ample variations exist in the tandem (gt)n and (ga)m dinucleotides and especially their "degenerated" derivatives. Phylogenetic trees for the alpha-helices and beta-pleated sheets of the ungulate DRB sequences suggest different evolutionary histories. In hoofed animals as well as in humans DRB beta-sheet encoding sequences and adjacent intronic repeats can be assembled into virtually identical groups suggesting coevolution of noncoding as well as coding DNA. In contrast alpha-helices and C-terminal parts of the first DRB domain evolve distinctly. In the absence of a defined mechanism causing specific, site-directed mutations, double-recombination or gene-conversion-like events would readily explain this fact. The role of the intronic simple (gt)n(ga)m repeat is discussed with respect to these genetic exchange mechanisms during evolution.

Alleles↗

PubMed1993

Structure and evolution of opossum, guinea pig, and porcupine cytochrome b genes.

We have sequenced the mitochondrial cytochrome b gene from the guinea pig, the African porcupine, and a South American opossum. A phylogenetic analysis, which includes 22 eutherian and four other vertebrate cytochrome b sequences, indicates that the guinea pig and the porcupine constitute a natural clade (Hystricomorpha) that is not a sister group to the clade of mice and rats (Myomorpha). Therefore, the hypothesis that the Rodentia is paraphyletic receives additional support. The artiodactyls, the perissodactyls, and the cetaceans form a group that is separated from the primates and the rodents. The 26 sequences are used to study the structure/function relationships in cytochrome b, whose function is electron transport. Most of the amino acid residues involved in the two reaction centers are well conserved in evolution. The four histidines that are believed to ligate the two hemes are invariant among the 26 sequences, but their nearby residues are not well conserved in evolution. The eight transmembrane domains represent some of the most divergent regions in the cytochrome b sequence. The rate of nonsynonymous substitution is considerably faster in the human and elephant lineages than in other eutherian lineages; the faster rate might be due to coevolution between cytochrome b and cytochrome c.

Amino Acid Sequence↗

PubMed1987

Gradients for the evolution of bimatrix games.

The evolutionary dynamics of bimatrix games is studied for rescaled partnership games and zero sum games. The former case leads to gradient systems. The selection equations for sexual and asexual reproduction of genotypes corresponding to mixed strategies are analysed. As examples, the origin of anisogamy and cyclic chases for predator-prey coevolution are studied.

Animals↗

PubMed1991

Polymorphism within the nuclear and 2 micron genomes of Saccharomyces cerevisiae.

Seven strains of bakers' yeast were obtained as a representative sample of the Spanish baking industry. The nuclear genome was monitored for polymorphism by transverse alternating field electrophoresis (TAFE) and restriction maps of 2 micron DNA were produced. All seven strains were uniquely different when evaluated by their total chromosomal lengths whereas only two 2 micron variants were defined. There was no apparent correlation between chromosomal and plasmid polymorphism. The extensive chromosomal polymorphism within one 2 micron DNA type indicates the rapid and relatively recent evolution of the nuclear genome. The hybrid origin (S. cerevisiae-S. monacensis) of lager yeast was critically evaluated by TAFE analysis of S. cerevisiae and S. carlsbergensis chromosomes. The absence of corresponding S. cerevisiae chromosomes III and XIII in S. carlsbergensis argued against the hybrid origin of lager strains. We discuss limitations of the hybrid origin hypothesis of industrial yeasts and propose that the molecular coevolution observed in 2 micron DNA serves as a useful additional mechanism for rationalization of some of the structural polymorphism of the nuclear genome.

Chromosomes, Fungal↗

PubMed1980

Atmospheric constraints on the evolution of metabolism.

Earth's early history may have been characterized by coevolution of microbial metabolism and atmospheric composition. Metabolic developments affected the composition of the atmosphere and the resultant changes in the atmosphere stimulated the evolution of new metabolic capabilities. The first organisms were presumably fermenting heterotrophs, exploiting organic molecules abiotically synthesized. These organisms multiplied, developing new biosynthetic capabilities to overcome deficiencies in the abiotic supply of particular compounds, until their growth was limited by the energy source provided by abiotic synthesis of fermentable organic compounds. Further growth required a new energy source, which may have been the chemical energy represented by the mixture of carbon dioxide and hydrogen in the primitive atmosphere. Chemotrophic organisms resembling methane bacteria may have evolved to exploit this source. They would have flourished, along with the heterotrophs that fed on them, until they had decreased the level of atmospheric hydrogen to the point where further extractions of chemical energy from the atmosphere was not possible. Once again, the expansion of life was limited by the availability of energy. The origin of bacterial photosynthesis overcame the second energy crisis. Photosynthetic bacteria could exploit the abundant energy of sunlight while using atmospheric hydrogen and reduced compounds derived from it only as electron donors. Life flourished again, drawing atmospheric hydrogen (replenished only by volcanoes) down to levels so low as to limit even bacterial photosynthesis. Before the full potential of photosynthesis could be exploited the evolution of the metabolic apparatus to process an electron donor of unlimited abundance was necessary. This donor, of course, was water, and the new metabolic process was algal photosynthesis. The oxygen released changed the world from anaerobic to aerobic and made possible the last great advance in energy-yielding metabolism, aerobic respiration.

Aerobiosis↗

PubMed1993

Female song preference and the period gene in Drosophila.

Mutations at the period (per) locus in Drosophila melanogaster alter rhythmic components of the male courtship song. We have examined the mating speed of females homozygous for mutant per alleles when presented with artificial mutant songs. Mutant females retain a preference for wild-type over mutant songs, thus male song and female preference are probably under separate genetic control. In contrast, per-mutant females from an established laboratory stock which had been maintained for nearly two decades appear to have an enhanced response to the corresponding mutant song in that they no longer discriminate against mutant song. These results are discussed in terms of the "genetic coupling" and "coevolution" theories of complementarity between male and female components of communication system.

Animals↗

PubMed1992

Evolution of thymidine and thymidylate kinases: the possibility of independent capture of TK genes by different groups of viruses.

Phylogenetic analysis of viral and cellular thymidine and thymidylate kinases was performed using computer-assisted methods. Multiple alignments and tentative phylogenetic trees were generated for the two families of these enzymes, which include a) thymidine kinases (TK) of mammals, poxviruses, African swine fever virus, E. coli, and bacteriophage T4; and b) thymidylate kinases (ThyK) of yeast and poxviruses and distantly related herpesvirus proteins with both enzymatic activities. Analysis of the alignment of the TKs of the first family highlighted three strongly conserved segments. Two of these corresponded to the A and B motifs of the purine NTP-binding pattern. The third, C-terminal segment, showing the highest conservation, encompassed a modified Zn finger motif. It is speculated that this motif might be involved in TK oligomerization. Phylogenetic trees constructed by three different methods suggested that cellular TK genes could be captured independently by T4 bacteriophage, African swine fever virus, fowlpox virus, and the other poxviruses. The observed tree topologies appear to contradict the popular virus-host coevolution schemes and to imply that different subdivisions of poxviruses diverged at earlier stages of evolution than their hosts did. It was shown that deoxynucleoside monophosphate kinase of bacteriophage T4 is related to the ThyK family. Phylogenetic analysis suggested that ThyK genes probably have been acquired independently by phage T4, poxviruses, and herpes-viruses.

Amino Acid Sequence↗

PubMed1990

GC balance in the internal transcribed spacers ITS 1 and ITS 2 of nuclear ribosomal RNA genes.

The internal transcribed spacer (ITS) 1 and 2, the 5.8S rRNA gene, and adjacent 18S rRNA and 25S rRNA coding regions of two Cucurbitaceae (Cucurbita pepo, zucchini, ITS 1: 187 bp, and ITS 2: 252 bp in length, and Cucumis sativus, cucumber, ITS 1: 229 bp, and ITS 2: 245 bp in length) have been sequenced. The evolutionary pattern shown by the ITSs of these plants is different from that found in vertebrates. Deletions, insertions, and base substitutions have occurred in both spacers; however, it is obvious that some selection pressure is responsible for the preservation of stem-loop structures. The dissimilarity of the 5' region of ITS 2 found in higher plants has consequences for proposed models on U3 snRNA-ITS 2 interaction in higher eukaryotes. The two investigated Cucurbitaceae species show a G + C content of ITS 1 that nearly equals that of ITS 2. An analysis of the ITS sequences reveals that in 19 out of 20 organisms published, the G + C content of ITS 1 nearly equals that of ITS 2, although it ranges from 20% to 90% in different organisms (GC balance). Moreover, the balanced G + C content of the ITSs in a given species seems to be similar to that of so-called expansion segments (ESs) in the 25/28S rRNA coding region. Thus, ITSs show a phenomenon called molecular coevolution with respect to each other and to the ESs. In the ITSs of Cucurbitaceae the balanced G + C composition is at least partly achieved by C to T transitions, via deamination of 5-methylcytosine. Other mutational events must be taken into account. The appearance of this phenomenon is discussed in terms of functional constraints linked to the structures of these spacers.

Animals↗