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Rosemary J Redfield Wendy A Findlay Janine Bossé J Simon Kroll Andrew DS Cameron John HE Nash 《BMC evolutionary biology》2006,6(1):82-15
Background
Many bacteria can take up DNA, but the evolutionary history and function of natural competence and transformation remain obscure. The sporadic distribution of competence suggests it is frequently lost and/or gained, but this has not been examined in an explicitly phylogenetic context. Additional insight may come from the sequence specificity of uptake by species such as Haemophilus influenzae, where a 9 bp uptake signal sequence (USS) repeat is both highly overrepresented in the genome and needed for efficient DNA uptake. We used the distribution of competence genes and DNA uptake specificity in H. influenzae 's family, the Pasteurellaceae, to examine the ancestry of competence. 相似文献24.
25.
Repeated evolution of an acetate-crossfeeding polymorphism in long-term populations of Escherichia coli 总被引:1,自引:0,他引:1
Six out of 12 independent replicate populations of Escherichia coli
maintained in long-term glucose-limited continuous culture for up to
approximately 1,750 generations evolve polymorphisms maintained by acetate
crossfeeding. In all cases, the acetate-crossfeeding phenotype is
associated with semiconstitutive overexpression of acetyl CoA synthetase,
which allows for the enhanced uptake of low levels of exogenous acetate.
Mutations in the 5' regulatory region of the acetyl CoA synthetase locus
are responsible for all the acetate crossfeeding phenotypes found. These
changes were either transposable-element insertions or a single T-->A
nucleotide substitution at position -93 relative to the acs gene
translation start site.
相似文献
26.
Within-stem oxygen concentration and sap flow in four temperate tree species: does long-lived xylem parenchyma experience hypoxia? 总被引:6,自引:0,他引:6
Oxygen levels as low as 1–5% (gaseous mole fraction) occur in secondary xylem, but it is not known if there is a consistent pattern of decline in O2 from the cambium toward the pith, or whether parenchyma cells experience hypoxic conditions deep within the stem. We developed a system for repeated in situ measurement of O2 at different depths within stems of Acer rubrum, Fraxinus americana, Tsuga canadensis, and Quercus rubra. In summer during active transpiration, O2 declined from the cambium toward the heartwood boundary in F. americana, T. canadensis and Q. rubra, but remained constant in A. rubrum. Average sapwood O2 was about 10%, with the lowest values observed in the innermost sapwood around 3–5%. Before spring leaf flush, O2 content in the outer sapwood was reduced in Q. rubra and T. canadensis relative to summer, and was occasionally lower than in the inner sapwood. Sapwood respiration in T. canadensis was constant above 5% O2, but reduced by about 65% at 1% O2. In F. americana, sapwood respiration was constant above 10% O2 but reduced by 25% at 5% O2, and by 75% at 1% O2, the most extreme inhibition observed. However, when prolonged (72 h) exposure to 1%, 5% and 10% O2 was followed by re-equilibration to 10% O2, no inhibition was found. Given the minor (and reversible) effect of low O2 on parenchyma metabolism at levels common in the inner sapwood, it is unlikely that O2 content severely limits parenchyma respiration or leads to parenchyma cell death during sapwood senescence. Within-stem O2 levels may instead be most relevant to metabolism in the cambial zone and phloem, for which sapwood could serve as a significant source of O2. 相似文献
27.
Background
Extensive focus is placed on the comparative analyses of consensus genotypes in the study of West Nile virus (WNV) emergence. Few studies account for genetic change in the underlying WNV quasispecies population variants. These variants are not discernable in the consensus genome at the time of emergence, and the maintenance of mutation-selection equilibria of population variants is greatly underestimated. The emergence of lineage 1 WNV strains has been studied extensively, but recent epidemics caused by lineage 2 WNV strains in Hungary, Austria, Greece and Italy emphasizes the increasing importance of this lineage to public health. In this study we explored the quasispecies dynamics of minority variants that contribute to cell-tropism and host determination, i.e. the ability to infect different cell types or cells from different species from Next Generation Sequencing (NGS) data of a historic lineage 2 WNV strain.Results
Minority variants contributing to host cell membrane association persist in the viral population without contributing to the genetic change in the consensus genome. Minority variants are shown to maintain a stable mutation-selection equilibrium under positive selection, particularly in the capsid gene region.Conclusions
This study is the first to infer positive selection and the persistence of WNV haplotype variants that contribute to viral fitness without accompanying genetic change in the consensus genotype, documented solely from NGS sequence data. The approach used in this study streamlines the experimental design seeking viral minority variants accurately from NGS data whilst minimizing the influence of associated sequence error. 相似文献28.
29.
In an isolated population of Drosophila melanogaster on Ishigaki Island the
chromosomal distribution of several retrotransposons, including copia, 412,
297, 17.6, I, and jockey elements, was examined by in situ hybridization.
In this population the cosmopolitan inversion, In(2L)t, is known to exist
in high frequency. One major haplotype concerning the occupied sites of the
transposable elements was identified in the In(2L)t-carrying chromosomes.
This haplotype is suggested to be the ancestral one. The age of the
inversion in this local population was estimated to be 1,400 generations.
The transposition rates of these elements were estimated based on the age
of the inversion and the number of the elements lost and gained. The
excision rates were in the range from 9.13 x 10(-5) to 2.25 x 10(-4) per
site per generation. They were similar each other in the copia-like
elements as well as in the LINE-like elements. The rate was higher in the
copia-like elements than in the LINE-like elements. Insertions occurred in
the range from 6.79 x 10(-4) to 9.05 x 10(-4) per element per generation.
It is herein shown that both insertions and excisions occurred at a
significantly higher rate in this population than in the laboratory.
相似文献
30.
Two soluble glycosyltransferases glycosylate less efficiently in vivo than their membrane bound counterparts 总被引:2,自引:1,他引:1
Zhu G; Allende ML; Jaskiewicz E; Qian R; Darling DS; Worth CA; Colley KJ; Young WW Jr 《Glycobiology》1998,8(8):831-840
Many Golgi glycosyltransferases are type II membrane proteins which are
cleaved to produce soluble forms that are released from cells. Cho and
Cummings recently reported that a soluble form of alpha1, 3-
galactosyltransferase was comparable to its membrane bound counterpart in
its ability to galactosylate newly synthesized glycoproteins (Cho,S.K. and
Cummings,R.D. (1997) J. Biol. Chem., 272, 13622-13628). To test the
generality of their findings, we compared the activities of the full length
and soluble forms of two such glycosyltransferases, ss1,4
N-Acetylgalactosaminyltransferase (GM2/GD2/ GA2 synthase; GalNAcT) and beta
galactoside alpha2,6 sialyltransferase (alpha2,6-ST; ST6Gal I), for
production of their glycoconjugate products in vivo . Unlike the full
length form of GalNAcT which produced ganglioside GM2 in transfected cells,
soluble GalNAcT did not produce detectable GM2 in vivo even though it
possessed in vitro GalNAcT activity comparable to that of full length
GalNAcT. When compared with cells expressing full length alpha2,6-ST, cells
expressing a soluble form of alpha2,6-ST contained 3-fold higher
alpha2,6-ST mRNA levels and secreted 7-fold greater alpha2,6-ST activity as
measured in vitro , but in striking contrast contained 2- to 4-fold less of
the alpha2,6-linked sialic acid moiety in cellular glycoproteins in vivo .
In summary these results suggest that unlike alpha1,3-galactosyltransferase
the soluble forms of these two glycosyltransferases are less efficient at
glycosylation of membrane proteins and lipids in vivo than their membrane
bound counterparts.
相似文献