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排序方式: 共有523条查询结果,搜索用时 15 毫秒
1.
2.
Assembly of transcriptionally active chromatin in vitro: a possible role for topoisomerase II 总被引:2,自引:0,他引:2
Some models of in vitro chromatin assembly suggest a biphasic molecular mechanism. The first phase, nucleosome formation, is comprised of the formation of histone-DNA complexes which mature into a canonical nucleosome structure. The second phase represents the process by which these nucleosomes become properly spaced with a regular periodicity on the DNA. In this report, we examine the role of DNA topoisomerases in the latter phase of chromatin assembly. To study this process, we use a Xenopus laevis cell-free extract, which assembles quantitative amounts of chromatin on circular DNA templates, and the type II topoisomerase-specific antitumor drugs VM-26 and endrofloxicin. Our results suggest that nucleosome formation is unaffected by the presence of VM-26 or endrofloxicin. However, periodic spacing of nucleosomes is inhibited significantly by these drugs. In the absence of proper chromatin assembly, circular DNA molecules are processed into nucleoprotein complexes which are transcribed poorly. Taken together, these results indicate that the antitumor drugs VM-26 and endrofloxicin influence gene expression indirectly by blocking the periodic spacing of nucleosomes. 相似文献
3.
Some Properties of Extracellular Acetylxylan Esterase Produced by the Yeast Rhodotorula mucilaginosa
Lee H To RJ Latta RK Biely P Schneider H 《Applied and environmental microbiology》1987,53(12):2831-2834
The red yeast Rhodotorula mucilaginosa produced an esterase that accumulated in the culture supernatant on induction with triacetin. The enzyme was specific for substrates bearing an O-acetyl group, but was relatively nonspecific for the rest of the molecule, which could consist of a phenol, a monosaccharide, a polysaccharide, or an aliphatic alcohol. The esterase was more active against acetylxylan and glucose beta-d-pentaacetate than were a number of esterases from plant and animal sources, when activities on 4-nitrophenyl acetate were compared. The enzyme exhibited Michaelis-Menten kinetics and was active over a broad pH range (5.5 to 9.2), with an optimum between pH 8 and 10. In addition, the enzyme retained its activity for 2 h at 55 degrees C. The yeast that produced the enzyme did not produce xylanase and, hence, is of interest for the production of acetylxylan esterase that is free of xylanolytic activity. 相似文献
4.
K. -Y. To C. -C. Chen Y. -K. Lai 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,78(1):81-86
Summary Streptomycin-resistant colonies were isolated from protoplast cultures of haploid Nicotiana plumbaginifolia based on their ability to green in medium containing 1 mg/ml streptomycin sulfate. The frequency of resistant colonies was 0.9×10–5 in nonmutagenized culture, and increased ten-fold following treatment of culture with 10 g/ml N-methyl-N-nitro-N-nitrosoguanidine. Of a total of 52 resistant clones isolated, 2 gave rise to haploid, 15 to diploid, and 3 to tetraploid plants upon transfer of calli to differentiation medium. Leaf-segment and protoplast assays showed that all diploid regenerates were resistant to streptomycin but sensitive to chloramphenicol, kanamycin, lincomycin, neomycin, and spectinomycin. Plants in most diploid clones were fertile and able to set seeds when self-fertilized and crossed reciprocally to wild-type plants. Inheritance of streptomycin resistance was studied in the diploid clones and, without exception, the resistance was transmitted maternally. Comparative studies of the ultrastructure of organelles and protein synthesis in isolated chloroplasts between wild-type and resistant clones in the presence of streptomycin suggest that streptomycin resistance is controlled by chloroplasts. 相似文献
5.
6.
Human esterase D gene: complete cDNA sequence,genomic structure,and application in the genetic diagnosis of human retinoblastoma 总被引:4,自引:2,他引:2
Lih-Jiuan S. Young Eva Y. -H. P. Lee Hoang To Robert Bookstein Jin-Yuh Shew Larry A. Donoso Theodore Sery Michael Giblin Jerry A. Shields Wen-Hwa Lee 《Human genetics》1988,79(2):137-141
Summary The gene encoding human esterase D (EsD), a member of the nonspecific esterase family, is a useful genetic marker for retinoblastoma (RB) and Wilson's disease. Previously we identified a cDNA clone from this gene and determined its chromosomal location. In this report, we present the complete cDNA sequence of the human EsD gene. A long open reading frame encoded a predicted protein of 282 amino acids with molecular weight of 30 kD. A computer-assisted search of a protein sequence data base revealed homology with two other esterases, acetylcholinesterase of Torpedo and esterase-6 of Drosophila. Homologous region were centered around presumptive active sites, suggesting that the catalytic domains of the esterases are conserved during evolution. Three genomic clones of this gene were also isolated and characterized by restriction mapping. At least ten exons were distributed over a 35-kb (kilobase pair) region; each exon contained an average of 100 basepairs (bp). A polymorphic site for Apa I, located within an intron of the esterase D gene, can be used to identify chromosome 13 carrying defective RB alleles within retinoblastoma families. 相似文献
7.
Codon usage in the vertebrate hemoglobins and its implications 总被引:2,自引:0,他引:2
A study of codon usage in vertebrate hemoglobins revealed an evolutionary
trend toward elevated numbers of CpG codon boundary pairs in mammalian
hemoglobin alpha genes. Selection for CpG codon boundaries countering the
generally observed CpG suppression is strongly suggested by these data.
These observations parallel recently published experimental results that
indicate that constitutive expression of the human alpha-globin gene
appears to be determined by regulatory information encoded within the
structural gene. The possibility is raised that, in the absence of
selection, CpG decay can be used to date the evolutionary origin of a
mammalian alpha pseudogene from its active alpha gene.
相似文献
8.
Evolution of crystallins: expression of lens-specific proteins in the blind mammals mole (Talpa europaea) and mole rat (Spalax ehrenbergi) 总被引:3,自引:0,他引:3
Quax-Jeuken Y; Bruisten S; Bloemendal H; de Jong WW; Nevo E 《Molecular biology and evolution》1985,2(4):279-288
The mole (Talpa europaea; Insectivora) and the mole rat (Spalax ehrenbergi;
Rodentia) both have degenerated eyes as a convergent adaptation to
subterranean life. The rudimentary eye lenses of these blind mammals no
longer function in a visual process. The crystallin genes, which display a
lens-specific expression pattern, were studied in these blind mammals and
in related species with normal eyes by hybridizing their genomic DNAs with
probes obtained from cDNA clones for alpha A-, alpha B-, and beta
Bp-crystallins from calf and gamma 3- crystallin from the rat. For all
crystallin genes examined, the hybridization signals of mole and mole rat
genomic DNA were comparable, respectively, with those of shrew and of rat
and mouse, normal-vision representatives of the orders Insectivora and
Rodentia. The expression of the crystallins at the protein level was tested
by using antiserum specific for alpha-crystallin in immunofluorescence
reactions on lens sections of mole and mole rat eyes and by using antisera
against the beta- and gamma-crystallins on sections of the mole eye. All
antisera gave positive fluorescence reactions exclusively with lens tissue
of these blind mammals, indicating that the crystallins are still normally
expressed despite the fact that these lenses have had no function in a
visual process in these mammals for at least many million years. These
findings apparently imply that some unknown selective advantage has
conserved the crystallin genes and their expression after the loss of
normal function of the lenses.
相似文献
9.
Alysiella bovis adheres to surfaces by means of short, ruthenium red-staining, rod-like fimbriae. The fimbriae remain associated with the cell envelope of A. bovis, even when sonicated or exposed sequentially to toluene, Triton X-100, lysozyme, ribonuclease, and deoxyribonuclease. Adhesion of outer membrane-derived cell wall ghosts of A. bovis to glass was inhibited by IO4-, sodium dodecyl sulfate, urea, pronase, and trypsin. Protease treatment digested the fimbriae from the distal end, and exposure to sodium dodecyl sulfate depolymerized the fimbriae. Exposure of ghosts to 1% sodium dodecyl sulfate preferentially solubilized a 16,500-dalton protein which was subsequently purified by gel filtration and demonstrated to be a glycoprotein (ca. 17% carbohydrate). Antibodies raised against the 16,500-dalton glycoprotein agglutinated whole cells and inhibited adhesion of ghosts to glass. 相似文献
10.
In Drosophila pseudoobscura, the amylase (Amy) multigene family is
contained within a series of inversions, or gene arrangements, on the third
chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL)
inversions are central to the phylogeny of arrangements, and have clusters
of other arrangements derived from them. The gene arrangements belonging to
each of these three clusters have a characteristic number of Amy genes,
ranging from three in ST to two in SC to one in TL. This distribution
pattern can reflect a history of either duplications or deletions, although
the data available in the past did not permit a decision between these
alternatives. We provide unambiguous evidence that three Amy genes were
present before the divergence of the ST, SC, and TL arrangements. Thus, the
current status of the Amy multigene family is the result of deletions in
the TL and SC arrangements, which created three new pseudogenes: TL
Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences
revealed that, in the SC and ST arrangements, pseudogene evolution has been
retarded, most likely due to the homogenization effect of gene conversion.
Finally, by determining the original copy number, we have reconstructed the
evolutionary history of the Amy multigene family and linked it with the
evolution of the central gene arrangements.
相似文献