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1.
Total amplified DNA in methotrexate-resistant mouse lymphoma EL4 cells and mouse melanoma PG19 cells has been characterized in two ways. Metaphase spreads show the presence of additional chromosome forms that are either “homogeneously staining” chromosomes or “double minute” and ring chromosomes. Gel electrophoresis of restriction enzyme-digested nuclear DNA shows the presence of amplified sequences, the pattern of which is unique in each of five cell lines. We conclude that extensive DNA rearrangement has taken place during amplification. 相似文献
2.
Different subfamilies of alphoid repetitive DNA are present on the human and chimpanzee homologous chromosomes 21 and 22. 总被引:5,自引:1,他引:4 下载免费PDF全文
The alphoid repeat DNA on chimpanzee chromosome 22 was compared with alphoid repeat DNA on its human homologue, chromosome 21. Hybridization of different alphoid probes under various conditions of stringency show that the alphoid repeats of chimpanzee chromosome 22 are not closely related to those of human chromosome 21. Sequence analysis of cloned dimer and tetramer EcoRI fragments from chimpanzee chromosome 22 confirm the low overall level of homology, but reveal the presence of several nucleotide changes which are exclusive to the chromosome 21 subfamily of human alphoid DNA. Southern blot analysis of alphoid repeat DNA on the chimpanzee X chromosome suggests this subfamily has been strongly conserved during and since the separation of chimpanzee and man although the two subfamilies can be distinguished on the basis of Taq I restriction fragments. 相似文献
3.
Linearized bovine papillomavirus type 1 (BPV-1) DNA was introduced into mouse C127 cells, where it recircularized and replicated as an intact monomeric, extrachromosomal circular form in the resulting transformants. These cells contained a mixture of complex high molecular weight forms that were converted to a linear form of approximately BPV-1 size upon digestion with an enzyme that cuts once within the BPV-1 genome. Further analysis of one of these cell lines revealed that these high molecular weight forms consisted of two components. One was detected on agarose gels as a diffuse smear of slow-migrating material representing linear forms that were tightly associated with host chromosomes, probably by integration. The second component was composed of discrete-sized oligomeric open and supercoiled extrachromosomal circular forms of up to approximately 48 X 10(3) base-pairs (6 tandemly linked BPV-1 genomes) in size. No catenated (interlocked) forms could be detected. 相似文献
4.
Summary We have screened a human genomic DNA library with an immunoglobulin (Ig) derived switch (S) region specific probe for homologous sequences. Five Ig independent phage clones were isolated and characterized. The S sequence homologous DNA fragments are short compared to the S region sequences. Ig independent S sequences are flanked by highly repetitive DNA elements and perfect inverted repeats can be demonstrated in their close vicinity. Using subclones of S homologous sequences restriction fragment length polymorphisms were shown within DNA of different T cell leukemias. Burkitt lyphhomas, lymphoblastoid cell lines, and DNA of healthy individuals. One of the five clones isolated with the S region probe was evidently localized to chromosome 2 and/or 40 and showed a complex hybridisation pattern with several different human DNAs. S homologous sequences of another clone are most likely localized on chromosome 1. It is possible that these Ig indenpendent S sequences have arisen by amplification and transposition and that they are involved in genetic recombination. 相似文献
5.
Population genetics and phylogenetics of DNA sequence variation at multiple loci within the Drosophila melanogaster species complex 总被引:14,自引:1,他引:13
Two regions of the genome, a 1-kbp portion of the zeste locus and a 1.1-
kbp portion of the yolk protein 2 locus, were sequenced in six individuals
from each of four species: Drosophila melanogaster, D. simulans, D.
mauritiana, and D. sechellia. The species and strains were the same as
those of a previous study of a 1.9-kbp region of the period locus. No
evidence was found for recent balancing or directional selection or for the
accumulation of selected differences between species. Yolk protein 2 has a
high level of amino acid replacement variation and a low level of
synonymous variation, while zeste has the opposite pattern. This contrast
is consistent with information on gene function and patterns of codon bias.
Polymorphism levels are consistent with a ranking of effective population
sizes, from low to high, in the following order: D. sechellia, D.
melanogaster, D.mauritiana, and D. simulans. The apparent species
relationships are very similar to those suggested by the period locus
study. In particular, D. simulans appears to be a large population that is
still segregating variation that arose before the separation of D.
mauritiana and D. sechellia. It is estimated that the separation of
ancestral D. melanogaster from the other species occurred 2.5-3.4 Mya. The
separations of D. sechellia and D. mauritiana from ancestral D. simulans
appear to have occurred 0.58- 0.86 Mya, with D. mauritiana having diverged
from ancestral D. simulans 0.1 Myr more recently than D. sechellia.
相似文献
6.
A double cable model of the myelinated human motor nerve fibre is presented. The model is based on the nodal and internodal
channels in a previous, two-component model of human motor axons (Bostock et al. 1991), added to a complex extended cable
structure of nodal, paranodal and internodal segments. The model assumes a high-resistance myelin sheath and a leakage pathway
to the internodal axolemma via the paranodal seal resistance and periaxonal space. The parameter values of the model were
adjusted to match the recordings of threshold electrotonus in human motor fibres from Bostock et al. (1991). Kirchoff ’s current
law was used to derive a system of partial differential equations for the electrical equivalent circuit, and numerical integration
was performed with a fixed time increment and non-uniform spatial step sizes, in accordance with the complex structure of
the fibre. The model calculations provide estimates of the spatial and temporal distributions of action potentials and their
transaxonal and transmyelin components, both in different segments of the fibre and at different moments during action potential
propagation. The distribution of transaxonal and transmyelin currents along the fibre and their contributions from different
ionic channels are also explored.
Received: 14 July 1994/Accepted in revised form: 4 April 1995 相似文献
7.
8.
A study of sequence homologies in four satellite DNAs of man. 总被引:4,自引:0,他引:4
Satellites I, II, III and IV (Corneo et al., 1968,1970,1971) have been purified from human male placental DNA. The sequences present in these four DNA components have been characterized by analytical buoyant density, thermal denaturation, DNA reassociation, DNA hybridization and gel electrophoresis coupled with hybridization following either HaeIII or EcoRI restriction endonuclease digestion. Satellites III and IV were found to be virtually indistinguishable by a variety of criteria. Cross-satellite reassociation showed that 40% of the molecules present in satellite III contain sequences that are homologous to 10% of the molecules of either satellite I or satellite II. Reassociated satellite I melts as a single component, as do the hybrid duplexes between satellite I and satellite III. In contrast, reassociated satellites II, III and IV, and the hybrid duplexes formed between satellites II and III and between satellites II and IV, melt as two distinct components with different thermal stabilities.Digestion of satellite III with HaeIII gives rise to a series of fragments whose sizes are 2, 3, 4, 5, 6, 7, 8 and 11 times the size of the smallest 0.17 × 103 basepair fragment, in addition to a 3.4 × 103 base-pair male-specific fragment (Cooke, 1976) and high molecular weight material. The sequences contained in the fragments of the HaeIII ladder are diverged from each other as well as being non-homologous with those of the 3.4 × 103 base-pair and high molecular weight fragments. The latter contain EcoRI recognition sites. Satellite II has a similar pattern of fragments to satellite III following digestion with HaeIII, although it can be distinguished from satellite III on the basis of the products of EcoRI digestion. Satellite I contains neither HaeIII nor EcoRI recognition sites. The cross-satellite homologies of the sequences present in fragments of differing sizes produced by restriction enzyme digestion have also been studied. 相似文献
9.
10.
Rapid In Situ Assay for Indoleacetic Acid Production by Bacteria Immobilized on a Nitrocellulose Membrane 总被引:8,自引:2,他引:6 下载免费PDF全文
We have developed a new assay that differentiates between indoleacetic acid (IAA)-producing and -nonproducing bacteria on a colony plate lift. Medium supplemented with 5 mM L-tryptophan is inoculated with isolates of interest, overlaid with a nitrocellulose membrane, and then incubated until bacterial colonies reach 1 to 2 mm in diameter. The membrane is removed to a filter paper saturated with Salkowski reagent and incubated until distinct red haloes form around the colonies. The colorimetric reaction to IAA is limited to a region immediately surrounding each colony, is specific to isolates producing IAA, occurs within 1 h after the membrane is placed in the reagent, and is sensitive to as little as 50 pmol of IAA in a 2-mm2 spot. We have used this assay for quantifying epiphytic and endophytic populations of IAA-producing isolates of Pseudomonas syringae subsp. savastanoi and for detecting IAA-producing colonies of other pseudomonads and Erwinia herbicola. The assay provides a rapid and convenient method to screen large numbers of bacteria. 相似文献