2,768 research outputs found

    Molecular phylogenetics of Trypanosomatidae: contrasting results from 18S rRNA and protein phylogenies

    Get PDF
    Phylogenetic analyses of the family Trypanosomatidae have been conducted using both 18S rRNA gene sequences and a variety of protein sequences. Using a variety of phylogenetic methods, 18S rRNA phylogenies indicate that the genus Trypanosoma is not monophyletic. Rather, they suggest that the American and African trypanosomes constitute distinct clades. By contrast, phylogenetic analyses of available sequences in 42 protein families gene generally supported monophyly of the genus Trypanosoma. One possible explanation for these conflicting results is poor taxon sampling in the case of protein coding genes, most of which have been sequenced for only a few species of Trypanosomatidae

    DNA repeat arrays in chicken and human genomes and the adaptive evolution of avian genome size

    Get PDF
    BACKGROUND: Birds have smaller average genome sizes than other tetrapod classes, and it has been proposed that a relatively low frequency of repeating DNA is one factor in reduction of avian genome sizes. RESULTS: DNA repeat arrays in the sequenced portion of the chicken (Gallus gallus) autosomes were quantified and compared with those in human autosomes. In the chicken 10.3% of the genome was occupied by DNA repeats, in contrast to 44.9% in human. In the chicken, the percentage of a chromosome occupied by repeats was positively correlated with chromosome length, but even the largest chicken chromosomes had repeat densities much lower than those in human, indicating that avoidance of repeats in the chicken is not confined to minichromosomes. When 294 simple sequence repeat types shared between chicken and human genomes were compared, mean repeat array length and maximum repeat array length were significantly lower in the chicken than in human. CONCLUSIONS: The fact that the chicken simple sequence repeat arrays were consistently smaller than arrays of the same type in human is evidence that the reduction in repeat array length in the chicken has involved numerous independent evolutionary events. This implies that reduction of DNA repeats in birds is the result of adaptive evolution. Reduction of DNA repeats on minichromosomes may be an adaptation to permit chiasma formation and alignment of small chromosomes. However, the fact that repeat array lengths are consistently reduced on the largest chicken chromosomes supports the hypothesis that other selective factors are at work, presumably related to the reduction of cell size and consequent advantages for the energetic demands of flight

    Polymorphism at the apical membrane antigen 1 locus reflects the world population history of Plasmodium vivax

    Get PDF
    <p>Abstract</p> <p>Background</p> <p>In malaria parasites (genus <it>Plasmodium</it>), <it>ama-1 </it>is a highly polymorphic locus encoding the Apical Membrane Protein-1, and there is evidence that the polymorphism at this locus is selectively maintained. We tested the hypothesis that polymorphism at the <it>ama-1 </it>locus reflects population history in <it>Plasmodium vivax</it>, which is believed to have originated in Southeast Asia and is widely geographically distributed. In particular, we tested for a signature of the introduction of <it>P. vivax </it>into the New World at the time of the European conquest and African slave trade and subsequent population expansion.</p> <p>Results</p> <p>One hundred and five ama<it>-1 </it>sequences were generated and analyzed from samples from six different Brazilian states and compared with database sequences from the Old World. Old World populations of <it>P. vivax </it>showed substantial evidence of population substructure, with high sequence divergence among localities at both synonymous and nonsynonymous sites, while Brazilian isolates showed reduced diversity and little population substructure.</p> <p>Conclusion</p> <p>These results show that genetic diversity in <it>P. vivax </it>AMA-1 reflects population history, with population substructure characterizing long-established Old World populations, whereas Brazilian populations show evidence of loss of diversity and recent population expansion.</p> <p>Note</p> <p>Nucleotide sequence data reported is this paper are available in the GenBank™ database under the accession numbers <ext-link ext-link-type="gen" ext-link-id="EF031154">EF031154</ext-link> – <ext-link ext-link-type="gen" ext-link-id="EF031216">EF031216</ext-link> and <ext-link ext-link-type="gen" ext-link-id="EF057446">EF057446</ext-link> – <ext-link ext-link-type="gen" ext-link-id="EF05487">EF057487</ext-link></p

    Reassortment of Ancient Neuraminidase and Recent Hemagglutinin in Pandemic (H1N1) 2009 Virus

    Get PDF
    Sequence analyses show that the outbreak of pandemic (H1N1) 2009 resulted from the spread of a recently derived hemagglutinin through a population of ancient and more diverse neuraminidase segments. This pattern implies reassortment and suggests that the novel form of hemagglutinin conferred a selective advantage

    Allelic Variation in the Circumsporozoite Protein of Plasmodium falciparum from Thai Field Isolates

    Get PDF
    Allelic variation in the Plasmodium falciparum circumsporozoite (CS) protein gene has been examined by sequencing the entire gene in 15 isolates from an endemic area of Thailand. The isolates contain a total of six new allelic forms of the tetrapeptide repeats and eight variants of the T cell epitope (TCE) region of the CS gene. All nucleotide substitutions in the TCE are nonsynonymous. There is no apparent association between the sequence patterns in the repeats and in the TCE. Comparison of the TCE with published sequences has shown that most variants of our isolates are not identical to those found in different geographic areas, suggesting geographic variation in genetic diversity of the CS protein. In a phylogenetic tree, the new Thai alleles did not cluster together, suggesting a considerable heterogeneity within some geographic areas. Furthermore, analyses of tetrapeptide repeats from a number of isolates and strains showed evidence of three genetic mechanisms for the generation of variation in the repeats of the CS gene: point mutation, duplication of one or more repeat units, and intragenic recombination

    A genome-wide screen identifies a single β-defensin gene cluster in the chicken: implications for the origin and evolution of mammalian defensins

    Get PDF
    BACKGROUND: Defensins comprise a large family of cationic antimicrobial peptides that are characterized by the presence of a conserved cysteine-rich defensin motif. Based on the spacing pattern of cysteines, these defensins are broadly divided into five groups, namely plant, invertebrate, α-, β-, and θ-defensins, with the last three groups being mostly found in mammalian species. However, the evolutionary relationships among these five groups of defensins remain controversial. RESULTS: Following a comprehensive screen, here we report that the chicken genome encodes a total of 13 different β-defensins but with no other groups of defensins being discovered. These chicken β-defensin genes, designated as Gallinacin 1–13, are clustered densely within a 86-Kb distance on the chromosome 3q3.5-q3.7. The deduced peptides vary from 63 to 104 amino acid residues in length sharing the characteristic defensin motif. Based on the tissue expression pattern, 13 β-defensin genes can be divided into two subgroups with Gallinacin 1–7 being predominantly expressed in bone marrow and the respiratory tract and the remaining genes being restricted to liver and the urogenital tract. Comparative analysis of the defensin clusters among chicken, mouse, and human suggested that vertebrate defensins have evolved from a single β-defensin-like gene, which has undergone rapid duplication, diversification, and translocation in various vertebrate lineages during evolution. CONCLUSIONS: We conclude that the chicken genome encodes only β-defensin sequences and that all mammalian defensins are evolved from a common β-defensin-like ancestor. The α-defensins arose from β-defensins by gene duplication, which may have occurred after the divergence of mammals from other vertebrates, and θ-defensins have arisen from α-defensins specific to the primate lineage. Further analysis of these defensins in different vertebrate lineages will shed light on the mechanisms of host defense and evolution of innate immunity

    Genomewide Pattern of Synonymous Nucleotide Substitution in Two Complete Genomes of Mycobacterium tuberculosis

    Get PDF
    Comparison of the pattern of synonymous nucleotide substitution between two complete genomes of Mycobacterium tuberculosis at 3,298 putatively orthologous loci showed a mean percent difference per synonymous site of 0.000328 ± 0.000022. Although 80.5% of loci showed no synonymous or nonsynonymous nucleotide differences, the level of polymorphism observed at other loci was greater than suggested by previous studies of a small number of loci. This level of nucleotide difference leads to the conservative estimate that the common ancestor of these two genotypes occurred approximately 35,000 ago, which is twice as high as some recent estimates of the time of origin of this species. Our results suggest that a large number of loci should be examined for an accurate assessment of the level of nucleotide diversity in natural populations of pathogenic microorganisms

    Casein Kinase II Phosphorylation of Spt6 Enforces Transcriptional Fidelity by Maintaining Spn1-Spt6 Interaction

    Get PDF
    Spt6 is a histone chaperone that associates with RNA polymerase II and deposits nucleosomes in the wake of transcription. Although Spt6 has an essential function in nucleosome deposition, it is not known whether this function is influenced by post-translational modification. Here, we report that casein kinase II (CKII) phosphorylation of Spt6 is required for nucleosome occupancy at the 5' ends of genes to prevent aberrant antisense transcription and enforce transcriptional directionality. Mechanistically, we show that CKII phosphorylation of Spt6 promotes the interaction of Spt6 with Spn1, a binding partner required for chromatin reassembly and full recruitment of Spt6 to genes. Our study defines a function for CKII phosphorylation in transcription and highlights the importance of post-translational modification in histone chaperone function
    corecore