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排序方式: 共有472条查询结果,搜索用时 15 毫秒
1.
2.
The Ade6-M26 Mutation of Schizosaccharomyces Pombe Increases the Frequency of Crossing over 总被引:6,自引:3,他引:3
The ade6-M26 mutation of Schizosaccharomyces pombe increases conversion frequency in comparison with the nearby mutation ade6-M375. In order to investigate the effect of ade6-M26 on crossover frequency, heteroallelic ade6 duplications were constructed by integration of plasmids carrying the marker gene ura4. One ade6 gene carries either of the mutations M26 or M375 while the other ade6 copy carries the L469 mutation in both duplications. The duplication with ade6-M26 yields Ade(+) recombinants at significantly higher frequencies in meiosis, but not in mitosis. Tetrad analysis and physical characterization of spore clones from recombination tetrads demonstrate that conversions, unequal crossovers and intrachromatid exchanges occur at higher frequencies but with unaltered proportions among them. The conversion events show a pronounced bias when M26 is involved: they take place preferentially at the M26 allele. Thus the ade6-M26 mutation not only enhances conversion frequency as demonstrated before, but also crossover frequency. It displays the properties expected for a preferred site of initiation of general meiotic recombination. The duplications also yielded new information on ectopic recombination in S. pombe: ectopic crossovers occur in the duplications at much higher frequency than among naturally dispersed homologous sequences. 相似文献
3.
Philippe Szankasi Christof Gysler Ulrich Zehntner Urs Leupold Jürg Kohli Peter Munz 《Molecular & general genetics : MGG》1986,202(3):394-402
Summary Recombination between dispersed yet related serine tRNA genes of Schizosaccharomyces pombe does occur during mitosis but it is approximately three orders of magnitude less frequent than in meiosis. Two mitotic events have been studied in detail. In the first, a sequence of at least 18 nucleotides has been transferred from the donor sup3 gene on the right arm of chromosome I to the related acceptor gene sup12 on the left arm of the same chromosome, thereby leading to the simultaneous change of 8 bp in the acceptor gene. This event must be explained in terms of recombination rather than mutation. It is assumed that it represents mitotic gene conversion, although it was not possible to demonstrate that the donor gene had emerged unchanged from the event. The second case reflects an interaction between sup9 on chromosome III and sup3 on chromosome I. Genetic and physical analysis allows this event to be described as mitotic gene conversion associated with crossingover. The result of this event is a reciprocal translocation. No further chromosomal aberrations were found among an additional 700 potential intergenic convertants tested. Thus intergenic conversion is much less frequently associated with crossingover than allelic conversion. However, the rare intergenic conversion events associated with crossingover provide a molecular mechanism for chromosomal rearrangements. 相似文献
4.
5.
Vipin K. Paliwal Krishan K. Kohli Mridula Sharma Ravindra Nath 《Molecular and cellular biochemistry》1986,71(2):139-147
Metallothionein (MT) a low molecular weight, Cd-binding, cysteine rich, cytosolic protein has been isolated, purified and characterized from cadmium exposed Rhesus monkeys maintained on protein calorie malnourished (PCM) diet. Metallothionein was resolved into three isoforms i.e. MTa, MTb and MTVc. The ratio of Cd, Zn and Cu varied in these isometallothioneins. MTc was the major isometallothionein. UV Spectra of MTc revealed the presence of mercaptide bonds and absence of aromatic amino acids. These observations were further confirmed by amino acid analysis of MTc which demonstrated high cysteine content (22.6) followed by serine, glycine and lysine. The molecular weight of MTc as determined by gel filtration and amino acid analysis was 13000 and 6398 daltons respectively. This demonstrates that MTc is a non-globular ellipsoid polypeptide. MTc showed a unique property of binding selenium. Monkey liver metallothionein was immunologically identical with human metallothionein. All the characteristics of MTc obtained in the present study reveal a similarity between monkey and human metallothionein probably due to closer phylogenetic relationship between the two species. 相似文献
6.
Meiotic Behavior and Linkage Relationships in the Secondarily Homothallic Fungus Agaricus Bisporus 总被引:18,自引:1,他引:17
R. W. Kerrigan J. C. Royer L. M. Baller Y. Kohli P. A. Horgen J. B. Anderson 《Genetics》1993,133(2):225-236
This study followed the transmission of 64 segregating genetic markers to 52 haploid offspring, obtained from both homokaryotic and heterokaryotic meiospores, of a cross (AG 93b) of Agaricus bisporus, the commonly cultivated ``button mushroom.' The electrophoretic karyotypes of the AG 93b component nuclei were determined concurrently (n = 13). Eleven distinct linkage groups were identified by two-point analysis. DNA-DNA hybridization showed that nine of these corresponded to unique chromosome-sized DNAs. Two other chromosomal DNAs were marked with nonsegregating markers, including the rDNA repeat. Two remaining chromosomes remained unmarked but hybridized to repeated-sequence probes. Cross 93b had an essentially conventional meiosis in which both independent assortment and joint segregation of markers occurred, but in which crossing over was infrequent over much of the mapped genome. The 48 homokaryotic spore-offspring had overall crossover frequencies that were similar to, but possibly slightly less than, those of three homokaryon constituents of heterokaryotic spore-offspring. These data provide support for our earlier cytogenetic model of sporogenesis in A. bisporus, that explains why heterokaryotic spore-offspring usually appear to exhibit no recombination. No evidence favoring an alternative, mitotic model of sporogenesis was found. The resulting genetic map appears to survey the genome extensively and for the first time permits localization of loci determining economically important traits in this fungal crop species. Large differences in the vigor of homokaryotic offspring were correlated with the inheritance of certain chromosome segments and were also often associated with significant departures from Mendelian segregation ratios. 相似文献
7.
Hot Spots of Recombination in Fission Yeast: Inactivation of the M26 Hot Spot by Deletion of the Ade6 Promoter and the Novel Hotspot Ura4-Aim 总被引:3,自引:2,他引:1
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The M26 mutation in the ade6 gene of Schizosaccharomyces pombe creates a hot spot of meiotic recombination. A single base substitution, the M26 mutation is situated within the open reading frame, near the 5' end. It has previously been shown that the heptanucleotide sequence 5' ATGACGT 3', which includes the M26 mutation, is required for hot spot activity. The 510-bp ade6-delXB deletion encompasses the promoter and the first 23 bp of the open reading frame, ending 112 bp upstream of M26. Deletion of the promoter in cis to M26 abolishes hot spot activity, while deletion in trans to M26 has no effect. Homozygous deletion of the promoter also eliminates M26 hot spot activity, indicating that the heterology created through deletion of the promoter per se is not responsible for the loss of hot spot activity. Thus, DNA sequences other than the heptanucleotide 5' ATGACGT 3', which must be located at the 5' end of the ade6 gene, appear to be required for hot spot activity. While the M26 hotspot stimulates crossovers associated with M26 conversion, it does not affect the crossover frequency in the intervals adjacent to ade6. The flanking marker ura4-aim, a heterology created by insertion of the ura4(+) gene upstream of ade6, turned out to be a hot spot itself. It shows disparity of conversion with preferential loss of the insertion. The frequency of conversion at ura4-aim is reduced when the M26 hot spot is active 15 kb away, indicating competition for recombination factors by hot spots in close proximity. 相似文献
8.
Takashi Ueda Yoshihiro Kohli Yoshimichi Abe Takuji Katoh Takeshi Ogasawara Yoshiaki Nojyo Kei Kashima 《Histochemistry and cell biology》1995,103(1):11-17
We evaluated the conditions of fixation for ultrastructurally demonstrating the endogenous peroxidase (PO) activity of macrophages in biopsied human liver. The application of microwaving and immersion fixation with tannic acid and aldehydes allowed excellent visualization of PO activity in the nuclear envelope (NE), rough endoplasmic reticulum (rER), and cytoplasmic granules (CG), with good preservation of cellular ultrastructures. The macrophages with PO activity showed one of the following five patterns of PO localization: positive in both the NE and rER but negative in the CG (type 1); negative in both the NE and rER but positive in the CG (type 2); negative in the NE but positive in both the rER and CG (type 3); positive in all three (type 4); PO negative (type 5). The type 1 cells resembled typical Kupffer cells, type 2 cells monocytes, and type 3 and 4 cells the exudate-resident macrophages considered to be a transitional form between exudate and resident macrophages. Type 5 cells may also be a transitional form between the exudate and resident macrophage, or an end-stage macrophage derived from exudate macrophages which have lost their PO activity. Tannic-acid-aldehyde immersion fixation with microwaving may be a useful method in the study of the PO activities of macrophages in biopsied human liver specimens. 相似文献
9.
R H Stellwagen R D Sailor K K Kohli 《Biochemical and biophysical research communications》1977,78(4):1162-1167
The following inhibitors of cyclic nucleotide phosphodiesterase reduce the specific activity of tyrosine aminotransferase when added to cultures of rat hepatoma (HTC) cells: theophylline, 1-methyl-3-isobutylxanthine, 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone, and papaverine. Immunochemical measurements show that each inhibitor reduces the rate of tyrosine aminotransferase synthesis and increases the rate of degradation of the enzyme. The effect on synthesis also occurs with general proteins while that on degradation appears specific for tyrosine aminotransferase. 相似文献
10.
Usage of the three termination codons in a single eukaryotic cell, the Xenopus laevis oocyte. 总被引:5,自引:3,他引:2
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M Bienz E Kubli J Kohli S deHenau G Huez G Marbaix H Grosjean 《Nucleic acids research》1981,9(15):3835-3850
Oocytes from Xenopus laevis were injected with purified amber (UAG), ochre (UAA), and opal (UGA) suppressor tRNAs from yeasts. The radioactively labeled proteins translated from the endogenous mRNAs were then separated on two-dimensional gels. All three termination codons are used in a single cell, the Xenopus laevis oocyte. But a surprisingly low number of readthrough polypeptides were observed from the 600 mRNAs studied in comparison to uninjected oocytes. The experimental data are compared with the conclusions obtained from the compilation of all available termination sequences on eukaryotic and prokaryotic mRNAs. This comparison indicates that the apparent resistance of natural termination codons against readthrough, as observed by the microinjection experiments, cannot be explained by tandem or very close second stop codons. Instead it suggests that specific context sequences around the termination codons may play a role in the efficiency of translation termination. 相似文献