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排序方式: 共有77条查询结果,搜索用时 15 毫秒
1.
Jeff A Johnson Heather RL Lerner Pamela C Rasmussen David P Mindell 《BMC evolutionary biology》2006,6(1):65-12
Background
Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis. 相似文献2.
Intron sequence and structure requirements for tRNA splicing in Saccharomyces cerevisiae 总被引:7,自引:0,他引:7
Predicted single-stranded structure at the 3' splice site is a conserved feature among intervening sequences (IVSs) in eukaryotic nuclear tRNA precursors. The role of 3' splice site structure in splicing was examined through hexanucleotide insertions at a central intron position in the Saccharomyces cerevisiae tRNA gene. These insertions were designed to alter the structure at the splice site without changing its sequence. Endonuclease cleavage of pre-tRNA substrates was then measured in vitro, and suppressor activity was examined in vivo. A precursor with fully double-stranded structure at the 3' splice site was not cleaved by endonuclease. The introduction of one unpaired nucleotide at the 3' splice site was sufficient to restore cleavage, although at a reduced rate. We have also observed that guanosine at the antepenultimate position provides a second consensus feature among IVSs in tRNA precursors. Point mutations at this position were found to affect splicing although there was no specific requirement for guanosine. These and previous results suggest that elements of secondary and/or tertiary structure at the 3' end of IVSs are primary determinants in pre-tRNA splice site utilization whereas specific sequence requirements are limited. 相似文献
3.
4.
Summary Ammonium nitrate fertilizer, labelled with15N, was applied in spring to winter wheat growing in undisturbed monoliths of clay and sandy loam soil in lysimeters; the rates
of application were respectively 95 and 102 kg N ha−1 in the spring of 1976 and 1975. Crops of winter wheat, oilseed rape, peas and barley grown in the following 5 or 6 years
were treated with unlabelled nitrogen fertilizer at rates recommended for maximum yields. During each year of the experiments
the lysimeters were divided into treatments which were either freelydrained or subjected to periods of waterlogging. Another
labelled nitrogen application was made in 1980 to a separate group of lysimeters with a clay soil and a winter wheat crop
to study further the uptake of nitrogen fertilizer in relation to waterlogging.
In the first growing season, shoots of the winter wheat at harvest contained 46 and 58% of the fertilizer nitrogen applied
to the clay and sandy loam soils respectively. In the following year the crops contained a further 1–2% of the labelled fertilizer,
and after 5 and 6 years the total recoveries of labelled fertilizer in the crops were 49 and 62% on the clay and sandy loam
soils respectively.
In the first winter after the labelled fertilizer was applied, less than 1% of the fertilizer was lost in the drainage water,
and only about 2% of the total nitrogen (mainly nitrate) in the drainage water from both soils was derived from the fertilizer.
Maximum annual loss occurred the following year but the proportion of tracer nitrogen in drainage was nevertheless smaller.
Leaching losses over the 5 and 6 years from the clay and sandy loam soil were respectively 1.3 and 3.9% of the original application.
On both soils the percentage of labelled nitrogen to the total crop nitrogen content was greater after a period of winter
waterlogging than for freely-drained treatments. This was most marked on the clay soil; evidence points to winter waterlogging
promoting denitrification and the consequent loss of soil nitrogen making the crop more dependent on spring fertilizer applications. 相似文献
5.
6.
alpha 1-Proteinase inhibitor (alpha 1-PI), a member of the serine
proteinase inhibitor superfamily, has a primary role in controlling
neutrophil elastase activity within the mammalian circulation. Several
studies have indicated that the reactive center region of alpha 1-PI, the
amino acid sequence of which is critical to recognition of and binding to
target proteinases, is highly divergent within and among species. This
appears to be a consequence of accelerated rates of evolution that may have
been driven by positive Darwinian selection. In order to examine this and
other features of alpha 1-PI evolution in more detail, we have isolated and
sequenced cDNAs representing alpha 1- PI mRNAs of the mouse species Mus
saxicola and Mus minutoides and have compared these with a number of other
mammalian alpha 1-PI mRNAs. Relative to other mammalian mRNAs, the extent
of nonsynonymous substitution is generally high throughout the alpha 1-PI
mRNA molecule, indicating greater overall rates of amino acid substitution.
Within and among mouse species, the 5'-half of the mRNA, but not the
3'-half, has been homogenized by concerted evolution. Finally, the reactive
center is under diversifying or positive Darwinian selection in murid
rodents (rats, mice) and guinea pigs yet is under purifying selection in
primates and artiodactyls. The significance of these findings to alpha 1-PI
function and the possible selective forces driving evolution of serpins in
general are discussed.
相似文献
7.
Mitochondrial DNA polymorphisms in subterranean mole-rats of the Spalax ehrenbergi superspecies in Israel, and its peripheral isolates 总被引:1,自引:0,他引:1
Nevo E; Honeycutt RL; Yonekawa H; Nelson K; Hanzawa N 《Molecular biology and evolution》1993,10(3):590-604
Patterns of mitochondrial DNA (mtDNA) variation were examined in 133
mole-rats constituting all four chromosomal species (2n = 52, 2n = 54, 2n =
58, and 2n = 60) of the Spalax ehrenbergi superspecies in Israel, as well
as the peripheral isolates of 2n = 60. In the main range of the complex, a
total of 28 mtDNA haplotypes were found in 64 mole-rats, with most
haplotypes being unique to either a single chromosomal species or
population. mtDNA divergence increased from low to high diploid number in a
north-to-south direction in Israel. Overall levels of mtDNA diversity were
unexpectedly the highest in the 2n = 60, the youngest species of the
complex. The mtDNA haplotypes can be separated into two major groups, 2n =
52-54 and 2n = 58-60, and a phylogenetic analysis for each group revealed
evidence of a few haplotypes not sorted by diploid number. The overall
patterns of mtDNA divergence seen within and among the four chromosomal
species are consistent with the parapatric mode of speciation as suggested
from previous studies of allozyme and DNA hybridization. In a separate data
set the patterns of mtDNA variation were examined across the main
geographic range and across peripheral semi-isolates and isolates of the 2n
= 60 chromosomal species. Fifteen haplotypes were found in 69 mole-rats.
High levels of mtDNA diversity characterized the main range, semi-isolated,
and even some desert isolated populations. The peripheral isolates contain
much mtDNA diversity, including novel haplotypes.
相似文献
8.
Paul W. Brandt-Rauf Gary Bomzer David Belford Matthew R. Pincus 《The protein journal》1991,10(4):437-441
Thebcr-abl chimeric gene of Philadelphia chromosome positive chronic myelogenous leukemias is only weakly transforming. This transformation activity is greatly enhanced by a Lys-for-Glu substitution at position 832 in the c-abl gene, as occurs in the highly transforming v-abl genes. It has been suggested that this mutation results in a significant structural change in the encoded protein product. Using conformational energy analysis, we have determined the allowed low-energy conformations for residues 828–836 of this protein with Lys and Glu at position 832. In both cases, the overwhelmingly preferred conformation for this region is a bend-helix motif. The helix terminates at residue 836, and there are no discernible differences in conformation between the Lys- and Glu-containing sequences. These results suggest that the activating amino acid substitution at position 832 in the c-abl protein product does not produce its effect via a local conformational change. 相似文献
9.
M F Crouch D A Belford P J Milburn I A Hendry 《Biochemical and biophysical research communications》1990,167(3):1369-1376
The contribution of the GTP-binding protein, Gi, to EGF, phorbol dibutyrate (PdBu)-, and insulin-stimulated DNA synthesis was examined in BALB/c3T3 cells. Pertussis toxin inhibited DNA synthesis by each agonist, particularly at suboptimal agonist concentrations, but the inhibition could be partially overcome with higher agonist concentrations and combinations of these agonists. This suggested that (1) some, but not all, of the mitogenic signals for all three agonists were transduced by Gi (2) Gi may be activated by post-receptor mechanisms involving protein kinase C. Gi alpha-specific antibodies and ADP-ribosylation by pertussis toxin using 32P-NAD each labelled a single protein band, representing one or more species of Gi alpha. Pertussis toxin treatment increased the synthesis of Gi alpha. These results are discussed in relation to possible direct effects of Gi alpha on nuclear control during division. 相似文献
10.