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1.
2.
MAJOR CLADES OF THE ANGIOSPERMS 总被引:2,自引:0,他引:2
ROLF DAHLGREN KÅRE BREMER 《Cladistics : the international journal of the Willi Hennig Society》1985,1(4):349-368
Abstract— Our knowledge of fundamental angiosperm interrelationships is still very incomplete. The absence of a narrowly circumscribed gymnosperm outgroup, ideally the sister group, makes character evaluation, necessary for a cladistic analysis, difficult. According to current views the superorder Magnoliiflorae with a number of other groups, for example the monocotyledons, may represent a complex of families near the base of the angiosperms. Interrelationships of groups within the monocotyledons are much better understood than those between groups within the dicotyledons. A cladogram of monocotyledon orders based on earlier work by R. Dahlgren, H. T. Clifford, and F. N. Rasmussen is presented. A data matrix for a sample of the angiosperms with 61 characters for 49 taxa, mostly magnoliifloran and related families, is presented. The characters are polarized mainly according to the current view that the primitive angiosperm morphotype is a woody dicotyledon with strobiloid flowers. As an alternative the matrix is adjusted following W. C. Burger's conjecture that the primitive angiosperm was a herbaceous monocotyledon with trimerous flowers. Both matrices were run in a computerized parsimony analysis, resulting in numerous equally parsimonious solutions. This result is illustrative of the great homoplasy in the available character information, and also of how little actually is known about fundamental angiosperm interrelationships or phylogeny. 相似文献
3.
Assignment of orthologous relationships among mammalian alpha-globin genes by examining flanking regions reveals a rapid rate of evolution 总被引:1,自引:0,他引:1
In order to study the relationships among mammalian alpha-globin genes, we
have determined the sequence of the 3' flanking region of the human alpha 1
globin gene and have made pairwise comparisons between sequenced
alpha-globin genes. The flanking regions were examined in detail because
sequence matches in these regions could be interpreted with the least
complication from the gene duplications and conversions that have occurred
frequently in mammalian alpha-like globin gene clusters. We found good
matches between the flanking regions of human alpha 1 and rabbit alpha 1,
human psi alpha 1 and goat I alpha, human alpha 2 and goat II alpha, and
horse alpha 1 and goat II alpha. These matches were used to align the
alpha-globin genes in gene clusters from different mammals. This alignment
shows that genes at equivalent positions in the gene clusters of different
mammals can be functional or nonfunctional, depending on whether they
corrected against a functional alpha-globin gene in recent evolutionary
history. The number of alpha-globin genes (including pseudogenes) appears
to differ among species, although highly divergent pseudogenes may not have
been detected in all species examined. Although matching sequences could be
found in interspecies comparisons of the flanking regions of alpha- globin
genes, these matches are not as extensive as those found in the flanking
regions of mammalian beta-like globin genes. This observation suggests that
the noncoding sequences in the mammalian alpha-globin gene clusters are
evolving at a faster rate than those in the beta-like globin gene clusters.
The proposed faster rate of evolution fits with the poor conservation of
the genetic linkage map around alpha-globin gene clusters when compared to
that of the beta-like globin gene clusters. Analysis of the 3' flanking
regions of alpha-globin genes has revealed a conserved sequence
approximately 100-150 bp 3' to the polyadenylation site; this sequence may
be involved in the expression or regulation of alpha-globin genes.
相似文献
4.
Isolation of intact Sm/RNP antigens from rabbit thymus 总被引:10,自引:0,他引:10
A comparison of the immunologically reactive components of the highly conserved Sm and RNP autoantigens from various mammalian tissue sources suggested the complete absence of a major 26K to 27K Sm-specific polypeptide in rabbit thymus extracts prepared by conventional procedures. A simple modification of the solubilization protocol, achieved by sonicating a suspension of commercial rabbit thymus acetone powder in 0.35 M NaCI, gave an extract containing the full complement of immunologically reactive Sm and RNP proteins detectable in other mammalian species. Without further manipulation, extracts were immediately passed through an immunoaffinity column constructed from human SLE IgG with both anti-Sm and anti-RNP reactivities. The proteins of the purified Sm/RNP were recovered in sufficient quantities for direct analysis by protein staining or immunoblot assays. The antigenic polypeptides were recovered intact and consisted of a single 73K RNP-specific species together with Sm-specific proteins of 26K to 27K (a doublet) and 13K. These proteins were easily visible by protein stain as were nonantigenic components of 35K, 32K, 11K, and less than 10K. The same polypeptides were present in affinity-purified Sm/RNP from HeLa cells, although the RNP protein was slightly smaller. The resolution and integrity of the complexes isolated by this simple two-step procedure, requiring less than 4 hr for completion, is remarkable, and the protein composition of the product compares quite favorably with antigens isolated from other sources by considerably more lengthy and laborious procedures. 相似文献
5.
6.
Torque generation in the flagellar motor of Escherichia coli: evidence of a direct role for FliG but not for FliM or FliN. 总被引:7,自引:4,他引:3 下载免费PDF全文
Among the many proteins needed for assembly and function of bacterial flagella, FliG, FliM, and FliN have attracted special attention because mutant phenotypes suggest that they are needed not only for flagellar assembly but also for torque generation and for controlling the direction of motor rotation. A role for these proteins in torque generation is suggested by the existence of mutations in each of them that produce the Mot- (or paralyzed) phenotype, in which flagella are assembled and appear normal but do not rotate. The presumption is that Mot- defects cause paralysis by specifically disrupting functions essential for torque generation, while preserving the features of a protein needed for flagellar assembly. Here, we present evidence that the reported mot mutations in fliM and fliN do not disrupt torque-generating functions specifically but, instead, affect the incorporation of proteins into the flagellum. The fliM and fliN mutants are immotile at normal expression levels but become motile when the mutant proteins and/or other, evidently interacting flagellar proteins are overexpressed. In contrast, many of the reported fliG mot mutations abolish motility at all expression levels, while permitting flagellar assembly, and thus appear to disrupt torque generation specifically. These mutations are clustered in a segment of about 100 residues at the carboxyl terminus of FliG. A slightly larger carboxyl-terminal segment of 126 residues accumulates in the cells when expressed alone and thus probably constitutes a stable, independently folded domain. We suggest that the carboxyl-terminal domain of FliG functions specifically in torque generation, forming the rotor portion of the site of energy transduction in the flagellar motor. 相似文献
7.
INTRODUCTI0NThedifferentiati0nofcelIsalongthemonocyte-macr0phagepathwayandthesig-nalsinvo1vedinthesecel1sacquiringtheabilitytokilltum0rcellsarenotfllllyundersto0d.Wehavebeenstudingamoleculewhichappearst0beanimportantmemberofthecytokinenetworkinvo1vedintheregulati0nmonocyteactivation.ThiscytokinetermedP48wasisolatedfr0mthehllmannullcellleukemiacell1ineReh.IthasbeenpurifiedtohomogeneityandfOundtobedistinctfrominterferongamma,col0nystimulatingfactors(CSFs)andTNFalphaalldbeta[1,2].Func-ti… 相似文献
8.
Interest among researchers in the diagnosis, aetiology, prevention, and treatment of root caries has increased substantially over the past two decades. However, there are some fundamental problems impeding the advancement of the field which remain to be addressed and resolved. A universally acceptable definition of root caries is not yet available. The relationship of root caries to coronal caries has not been established. The underlying disease process is still not clearly understood. The optimal utilisation of preventive/therapeutic agents for the treatment or prevention of root caries has not been determined. New treatment materials and preventive agents have not yet been tested in controlled clinical trials. These are a few of the issues and problems which we address in this paper. 相似文献
9.
New techniques for physical mapping of the human genome. 总被引:2,自引:0,他引:2
We describe improvements in techniques and strategies used for making maps of the human genome. The methods currently used are changing and evolving rapidly. Today's techniques can produce ordered arrays of DNA fragments and overlapping sets of DNA clones covering extensive genomic regions, but they are relatively slow and tedious. Methods under development will speed the process considerably. New developments include a range of applications of the polymerase chain reaction, enhanced procedures for high resolution in situ hybridization, and improved methods for generating, manipulating, and cloning large DNA fragments. More detailed genetic and physical maps will be useful for finding genes, including those associated with human diseases, long before the complete DNA sequence of the human genome is available. 相似文献
10.
The role of methionine in regulating folate-dependent reactions in isolated rat hepatocytes 总被引:3,自引:0,他引:3
In isolated rat hepatocytes, histidine and formate, are oxidized to CO2 by folate-dependent reactions. These reactions are stimulated two- to fourfold by the addition of l-methionine, dl-homocysteine, S-adenosyl-l-methionine (Ado-Met), or S-adenosyl-l-homocysteine (Ado-Hcy). These compounds all increase the hepatocyte concentration of Ado-Met and Ado-Hcy. Substrates of hepatic catechol O-methyltransferase, such as l-Dopa methyl ester and 3,4-dihydroxyphenylacetic acid, decrease the hepatocyte concentration of Ado-Met in the presence or absence of added l-methionine or dl-homocysteine. The catechols do not affect the concentration of Ado-Hcy, but they inhibit the oxidation of formate and histidine. Thus, there is an excellent positive correlation between the rate of histidine and formate oxidation and the concentration of Ado-Met. There is no correlation between the rate of these reactions and either the Ado-Hcy concentration or the concentration ratio of Ado-Met:Ado-Hcy. Ado-Met inhibition of rat hepatic 5,10-methylene tetrahydrofolate reductase activity is reversed by Ado-Hcy, but the dependency of rat hepatic 5-methyltetrahydrofolate-homocysteine transmethylase activity (methionine synthetase) on Ado-Met is not altered by Ado-Hcy. These results indicate that methionine, through its conversion to Ado-Met, regulates folate-dependent reactions in isolated hepatocytes by increasing activity of methionine synthetase which leads to an increased concentration of tetrahydrofolate. That methionine and Ado-Met increase the hepatocyte concentration of nonmethyltetrahydrofolate compounds and decrease the hepatocyte concentration of 5-methyltetrahydrofolate supports this hypothesis. 相似文献