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21.
Molecular evolution of mitochondrial 12S RNA and cytochrome b sequences in the pantherine lineage of Felidae 总被引:4,自引:2,他引:2
DNA sequence comparisons of two mitochondrial DNA genes were used to infer
phylogenetic relationships among 17 Felidae species, notably 15 in the
previously described pantherine lineage. The polymerase chain reaction
(PCR) was used to generate sequences of 358 base pairs of the mitochondrial
12S RNA gene and 289 base pairs of the cytochrome b protein coding gene.
DNA sequences were compared within and between 17 felid and five nonfelid
carnivore species. Evolutionary trees were constructed using phenetic,
cladistic, and maximum likelihood algorithms. The combined results
suggested several phylogenetic relationships including (1) the recognition
of a recently evolved monophyletic genus Panthera consisting of Panthera
leo, P. pardus, P. onca, P. uncia, P. tigris, and Neofelis nebulosa; (2)
the recent common ancestry of Acinonyx jubatus, the African cheetah, and
Puma concolor, the American puma; and (3) two golden cat species, Profelis
temmincki and Profelis aurata, are not sister species, and the latter is
strongly associated with Caracal caracal. These data add to the growing
database of vertebrate mtDNA sequences and, given the relatively recent
divergence among the felids represented here (1-10 Myr), allow 12S and
cytochrome b sequence evolution to be addressed over a time scale different
from those addressed in most work on vertebrate mtDNA.
相似文献
22.
The effects of pH and various salts upon the activity of a series of superoxide dismutases. 总被引:2,自引:0,他引:2 下载免费PDF全文
P O''Neill S Davies E M Fielden L Calabrese C Capo F Marmocchi G Natoli G Rotilio 《The Biochemical journal》1988,251(1):41-46
The CuZn superoxide dismutases (SODs) from ox, sheep, pig and yeast were investigated by pulse radiolysis in order to evaluate the role of electrostatic interactions between O2.- and SOD proteins in the mechanism of action of the SOD enzymes. The protein net charge in this series varies, as evaluated by the protein pI values spanning over a large range of pH: 8.0 (sheep), 6.5 (pig), 5.2 (ox) and 4.6 (yeast). The amino acid sequences are largely conserved, with the three mammalian proteins being highly homologous and the yeast protein having some distinct variations in the region surrounding the active site. At pH 8.0 the activities of the SODs from various sources are similar, though the minor differences observed suggest that in the highly homologous mammalian series the most acidic protein is the most enzymically efficient one. The pH-dependences of the various activities in the pH range 7-12 are similar, and the related curves are best fitted by two pK values, which are approx. 9.2 and 11.0 for the mammalian enzymes and 9.1 and 11.4 for the yeast enzyme. The activities of the proteins at I 0.1 are decreased by approx. 20% when compared with the activity at I 0.02 at pH 8.5, whereas at pH above 10 the pH-dependence of the activity approaches that determined at I 0.02 and at pH 11.9 the activity is essentially independent of ionic strength. The dependence upon ionic strength also depends on the salt used, with perchlorate being more effective than phosphate or borate or Mops and still effective at pH above 10.5, where the effect of other salts becomes negligible. The dual and concerted dependence of the activities of different SODs on pH and salt concentration is explained with the encounter of O2.- with the active-site copper being governed by the protonation of two positively charged groups in the vicinity of the active site. The gradient between these localized charges and the rest of the protein may explain the different activities of the mammalian proteins at lower pH. On the basis of the sequence variation of the SODs examined it is not possible to definitely identify these groups. Likely candidates are conserved basic amino acid side chains in the vicinity (less than or equal to 1.2 nm) of the active site, i.e. Lys-134 and Arg-141, but co-ordination of OH- in the first copper co-ordination sphere may be an additional factor accounting for the higher pK.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
23.
Alan Koller Malcolm A. O''Neill Alan G. Darvill Peter Albersheim 《Phytochemistry》1991,30(12):3903-3908
Suspension-cultured sycamore cells (Acer pseudoplatanus) were disrupted in aqueous K-Pi buffer and the insoluble residue (the cell wall) purified by extraction with organic solvents and air-dried (dry cell walls) or by washing with aqueous sodium dodecyl sulphate and stored frozen (wet cell walls). Polysaccharides solubilized from the purified wet and dry cell walls by enzymatic digestion and chemical extraction were isolated and their glycosyl-residue compositions compared. No significant differences were found in the types or yields of the polysaccharides solubilized by enzymatic digestion and chemical extraction of the wet and dry cell wall preparations. Moreover, the glycosyl-residue compositions of the so-called ‘-cellulose’ fraction that remains after extraction of the wet and dry cell wall preparations with alkali was indistinguishable from the glycosyl-residue compositions of the walls prior to extraction. 相似文献
24.
Background
Association mapping using abundant single nucleotide polymorphisms is a powerful tool for identifying disease susceptibility genes for complex traits and exploring possible genetic diversity. Genotyping large numbers of SNPs individually is performed routinely but is cost prohibitive for large-scale genetic studies. DNA pooling is a reliable and cost-saving alternative genotyping method. However, no software has been developed for complete pooled-DNA analyses, including data standardization, allele frequency estimation, and single/multipoint DNA pooling association tests. This motivated the development of the software, 'PDA' (Pooled DNA Analyzer), to analyze pooled DNA data. 相似文献25.
Localization of a protein-DNA interface by random mutagenesis. 总被引:2,自引:0,他引:2
The type I restriction and modification enzymes do not possess obvious DNA-binding motifs within their target recognition domains (TRDs) of 150-180 amino acids. To identify residues involved in DNA recognition, changes were made in the amino-TRD of EcoKI by random mutagenesis. Most of the 101 substitutions affecting 79 residues had no effect on the phenotype. Changes at only seven positions caused the loss of restriction and modification activities. The seven residues identified by mutation are not randomly distributed throughout the primary sequence of the TRD: five are within the interval between residues 80 and 110. Sequence analyses have led to the suggestion that the TRDs of type I restriction enzymes include a tertiary structure similar to the TRD of the HhaI methyltransferase, and to a model for a DNA-protein interface in EcoKI. In this model, the residues within the interval identified by the five mutations are close to the protein-DNA interface. Three additional residues close to the DNA in the model were changed; each substitution impaired both activities. Proteins from twelve mutants were purified: six from mutants with partial or wild-type activity and six from mutants lacking activity. There is a strong correlation between phenotype and DNA-binding affinity, as determined by fluorescence anisotropy. 相似文献
26.
Biological Activity of Reducing-End-Derivatized
Oligogalacturonides in Tobacco Tissue Cultures 总被引:4,自引:0,他引:4 下载免费PDF全文
Mark D. Spiro Brent L. Ridley Stefan Eberhard Keith A. Kates Yves Mathieu Malcolm A. O''Neill Debra Mohnen Jean Guern Alan Darvill Peter Albersheim 《Plant physiology》1998,116(4):1289-1298
The biological activity of reducing-end-modified oligogalacturonides was quantified in four tobacco (Nicotiana tabacum) tissue culture bioassays. The derivatives used were oligogalacturonides with the C-1 of their reducing end (a) covalently linked to a biotin hydrazide, (b) covalently linked to tyramine, (c) chemically reduced to a primary alcohol, or (d) enzymatically oxidized to a carboxylic acid. These derivatives were tested for their ability to (a) alter morphogenesis of N. tabacum cv Samsun thin cell-layer explants, (b) elicit extracellular alkalinization by suspension-cultured cv Samsun cells, (c) elicit extracellular alkalinization by suspension-cultured N. tabacum cv Xanthi cells, and (d) elicit H2O2 accumulation in the cv Xanthi cells. In all four bioassays, each of the derivatives had reduced biological activity compared with the corresponding underivatized oligogalacturonides, demonstrating that the reducing end is a key element for the recognition of oligogalacturonides in these systems. However, the degree of reduction in biological activity depends on the tissue culture system used and on the nature of the specific reducing-end modification. These results suggest that oligogalacturonides are perceived differently in each tissue culture system. 相似文献
27.
28.
Acceptor specificity of the human leukocyte alpha3 fucosyltransferase: role of FucT-VII in the generation of selectin ligands 总被引:2,自引:2,他引:0
Britten CJ; van den Eijnden DH; McDowell W; Kelly VA; Witham SJ; Edbrooke MR; Bird MI; de Vries T; Smithers N 《Glycobiology》1998,8(4):321-327
The alpha3 fucosyltransferase, FucT-VII, is one of the key
glycosyltransferases involved in the biosynthesis of the sialyl Lewis X
(sLex) antigen on human leukocytes. The sialyl Lewis X antigen
(NeuAcalpha(2-3)Galbeta(1-4)[Fucalpha(1-3)]GlcNAc-R) is an essential
component of the recruitment of leukocytes to sites of inflammation,
mediating the primary interaction between circulating leukocytes and
activated endothelium. In order to characterize the enzymatic properties of
the leukocyte alpha3 fucosyltransferase FucT-VII, the enzyme has been
expressed in Trichoplusia ni insect cells. The enzyme is capable of
synthesizing both sLexand sialyl-dimeric-Lexstructures in vitro , from
3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels
of fucose transfer observed to neutral or 3'-sulfated acceptors. Studies
using fucosylated NeuAcalpha(2-3)-(Galbeta(1- 4)GlcNAc)3-Me acceptors
demonstrate that FucT-VII is able to synthesize both di-fucosylated and
tri-fucosylated structures from mono- fucosylated precursors, but
preferentially fucosylates the distal GlcNAc within a polylactosamine
chain. Furthermore, the rate of fucosylation of the internal GlcNAc
residues is reduced once fucose has been added to the distal GlcNAc. These
results indicate that FucT-VII is capable of generating complex selectin
ligands, in vitro , however the order of fucose addition to the lactosamine
chain affects the rate of selectin ligand synthesis.
相似文献
29.
In spite of the increasing application of DNA fingerprinting to natural
populations and to the genetic identification of humans, explicit methods
for estimation of basic population genetic parameters from DNA
fingerprinting data have not been developed. Contributing to this omission
is the inability to determine, for multilocus fingerprinting probes,
relatively important genetic information, such as the number of loci, the
number of alleles, and the distribution of these alleles into specific
loci. One of the most useful genetic parameters that could be derived from
such data would be the average heterozygosity, which has traditionally been
employed to measure the level of genetic variation within populations and
to compare genetic variation among different loci. We derive here explicit
formulas for both the estimation of average heterozygosity at multiple
hypervariable loci and a maximum value for this estimate. These estimates
are based upon the DNA restriction-pattern matrices that are typical for
fingerprinting studies of humans and natural populations. For several
empirical data sets from our laboratory, estimates of average and maximal
heterozygosity are shown to be relatively close to each other. Furthermore,
variances of these statistics based on simulation studies are relatively
small. These observations, as well as consideration of the effect of
missing alleles and alternate numbers of loci, suggest that the average
heterozygosity can be accurately estimated using phenotypic DNA fingerprint
patterns, because this parameter is relatively insensitive to the lack of
certain genetic information.
相似文献
30.
Mammalian cells transformed by DNA and RNA tumor viruses are shown to display consistently different growth properties. All SV40, adenovirus type 7 and polyoma virus (DNA viruses) transformed cells propagated to high densities. The same cells transformed instead by RNA viruses: MSV strain Kirsten (MSV-Ki) or MSV strain Maloney (MSV-M) grew to densities which were consistently lower than DNA virus-transformed cells but greater than that of untransformed cells. The capacity to synthesize DNA at increasing densities also differentiated the RNA and DNA virus-transformed cells. As growing cultures of untransformed cells neared saturation density, the fraction of cells synthesizing DNA was minimal. The RNA virus-transformed cells were also contact-inhibited but at a significantly higher density. In contrast the DNA virus-transformed cells propagated to still greater densities and continued DNA synthesis at a high rate even at very high densities. Therefore the DNA virus-transformed cells truly are not contact inhibited. It is suggested that the capacity to continue DNA synthesis at high densities explains the attainment of much greater densities by DNA virus-transformed cells. There were no clear-cut differences in the ability to form colonies in agar, although a few of the RNA virus-transformed lines could not be propagated in semi-solid medium. These results may be explained as a persistence of the capacity of DNA tumor viruses to stimulate host cell DNA synthesis. 相似文献