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31.
A fast Monte Carlo integration algorithm with varying time step is described for cooperative binding of ligands of arbitrary length to a one-dimensional lattice. This algorithm is particularly suitable for strongly cooperative or anticooperative systems, i.e., when the time scales for different kinetic events are very different. As an application, the kinetics of a bimodal two-ligand system are briefly discussed. 相似文献
32.
G. B. Müller Johannes Streicher Romana J. Müller 《Development genes and evolution》1996,206(5):344-348
Homeosis, the ectopic formation of a body part, is one of the key phenomena that prompted the identification of the essential
selector genes controlling body organization. Shared elements of such homeotic genes exist in all studied animal classes,
but homeotic transformations of the same order of magnitude as in insects, such as the duplication of the thorax in Drosophila mutants, have not been described in vertebrates. Here we investigate the capacity of retinoic acid to modify tail regeneration
in amphibians. We show that retinoic acid causes the formation of an additional body segment in regenerating tails of Rana temporaria tadpoles. A second pelvic section, including vertebral elements, pelvic girdle elements and limb buds, forms at the mid-tail
level. This is the first report of a homeotic duplication of a whole body segment in vertebrate axial regeneration.
Received: 16 August 1996 / Accepted: 20 September 1996 相似文献
33.
Dieter Kreusch Johannes Lintig Joachim Schr?der 《Molecular & general genetics : MGG》1995,249(1):102-110
The occ and noc regions in octopine and nopaline Ti plasmids, respectively, are responsible for the catabolism of octopine and nopaline in Agrobacterium. The functions are activated in the presence of the opines by OccR and NocR, two related regulatory proteins, and the promoters contain common sequence motifs. We have investigated heterologous interactions between the regulators and the promoters. Previous experiments using all possible heterologous combinations of opines, regulators, and promoters in vivo had demonstrated that only the combination of nopalme, NocR, and the occ promoter led to limited promoter activation. We now show that OccR and NocR bind to the heterologous promoters in vitro and in vivo. The weak or non-existent promoter activation actually observed could be explained by the assumption that OccR and NocR use different activation mechanisms; we investigated protein-induced DNA bending because of reports that the two regulators differ in this respect. Analysis with a bending vector showed that both OccR and NocR induced a DNA bend that is relaxed in the presence of the respective opine. The data suggest that subtle differences in regulator/promoter interactions are responsible for the inactivity of the heterologous combinations. Investigations with a chimeric NocR/OccR protein indicated that it induced a DNA bend in both promoters. No opine-induced relaxation was detectable with the hybrid, and the inducible promoter was not activated. These findings suggest that bend relaxation may be an integral part of promoter activation. 相似文献
34.
Thomas Haaf A. Gregory Mater Johannes Wienberg David C. Ward 《Journal of molecular evolution》1995,41(4):487-491
CENP-B, a highly conserved centromere-associated protein, binds to -satellite DNA, the centromeric satellite of primate chromosomes, at a 17-bp sequence, the CENP-B box. By fluorescence in situ hybridization (FISH) with an oligomer specific for the CENP-B box sequence, we have demonstrated the abundance of CENP-B boxes on all chromosomes (except the Y) of humans, chimpanzee, pygmy chimpanzee, gorilla, and orangutan. This sequence motif was not detected in the genomes of other primates, including gibbons, Old and New World monkeys, and prosimians. Our results indicate that the CENP-B box containing subtype of -satellite DNA may have emerged recently in the evolution of the large-bodied hominoids, after divergence of the phylogenetic lines leading to gibbons and apes; the box is thus on the order of 15–25 million years of age. The rapid process of dispersal and fixation of the CENP-B box sequence throughout the human and great ape genomes is thought to be a consequence of concerted evolution of -satellite subsets on both homologous and nonhomologous chromosomes.Correspondence to: T. Haaf 相似文献
35.
Comparative chromosome painting between two marsupials: origins of an XX/XY1Y2 sex chromosome system
Roland Toder Rachel J. W. O’Neill Johannes Wienberg Patricia C. M. O’Brien Lucille Voullaire Jennifer A. Marshall-Graves 《Mammalian genome》1997,8(6):418-422
Cross-species chromosome painting was used to investigate genome rearrangements between tammar wallaby Macropus eugenii (2n = 16) and the swamp wallaby Wallabia bicolor (2n = 10♀/11♂), which diverged about 6 million years ago. The swamp wallaby has an XX female:XY1Y2 male sex chromosome system thought to have resulted from a fusion between an autosome and the small original X, not involving
the Y. Thus, the small Y1 should represent the original Y and the large Y2 the original autosome. DNA paints were prepared from flow-sorted and microdissected chromosomes from the tammar wallaby.
Painting swamp wallaby spreads with each tammar chromosome-specific probe gave extremely strong and clear signals in single-,
two-, and three-color FISH. These showed that two tammar wallaby autosomes are represented unchanged in the swamp wallaby,
two are represented by different centric fusions, and one by a tandem fusion to make the very long arms of swamp wallaby Chromosome
(Chr) 1. The large swamp wallaby X comprises the tammar X as its short arm, and a tandemly fused 7 and 2 as the long arm.
The acrocentric swamp wallaby Y2 is a 2/7 fusion, homologous with the long arm of the X. The small swamp wallaby Y1 is confirmed as the original Y by its painting with the tammar Y. However, the presence of sequences shared between the microdissected
tammar Xp and Y on the swamp wallaby Y2 implies that the formation of the compound sex chromosomes involved addition of autosome(s) to both the original X and Y.
We propose that this involved fusion with an ancient pseudoautosomal region followed by fission proximal to this shared region.
Received: 16 October 1996/Accepted: 30 January 1997 相似文献
36.
Summary A protocol for obtaining regenerated fertile plants from mesophyll protoplasts of three lines of Matthiola incana is described. Protoplasts were isolated from leaves of 21–28 days old Matthiola plants grown in controlled environment. Sustained divisions were achieved when protoplasts were embedded in sodium alginate. Up to 2.0 % of the protoplasts developed into colonies which could be transferred to shoot regeneration media. More than 25 % of the obtained calluses regenerated shoots. About 4 % of these shoots could be rooted and after transfer to soil phenotypically normal plants have been obtained.Abbreviations 2,4-D
2,4-dichlorphenoxyacetic acid
- NAA
naphthalene acetic acid
- IAA
indole-3-acetic acid
- BAP
6-banzylaminopurine
- IPA
isopentenyladenine
- IPAR
isopentenyladenosine
- MES
(2-[N-morpholino]) ethanesulfonic acid 相似文献
37.
38.
Jos C. F. M. Dreesen Joep P. M. Geraedts John C. M. Dumoulin Johannes L. H. Evers Math H. E. C. Pieters 《Human genetics》1995,96(3):323-329
In order to approach preimplantation testing for the fragile-X syndrome, we used genotyping of the polymorphic RS46(DXS548) locus closely linked to the FMR1 gene, in single reproductive cells of females. The RS46(DXS548) amplification was adjusted to the single cell level by a two-round polymerase chain reaction (PCR) procedure. Unfertilized oocytes and extruded polar bodies were subjected to PCR. RS46(DXS548) genotyping at the single cell level was successful in 95% of the samples. In two-third of the metaphase II oocytes and first polar bodies obtained from women who were heterozygous at the RS46(DXS548) locus, both maternal RS46(DXS548) alleles were observed because of crossing over during the first meiotic division. This makes gamete selection by first polar body analysis inefficient. From the allele frequencies found in 56 unrelated individuals, a heterozygote frequency of 51% was estimated, whereas the observed heterozygote frequency was 56%. The whole PCR procedure can be performed within 16 h after blastomere biopsy. Consequently, the selection and transfer of the diagnosed embryos can be carried out within an acceptable time. Therefore, preimplantation testing for the fragile-X syndrome with the RS46(DXS548) AC-repeat may be an alternative choice for prenatal testing for those carrier females who are heterozygous (informative) at the RS46(DXS548) locus. 相似文献
39.
Reproductive strategies of coastal marine fishes in the tropics 总被引:14,自引:0,他引:14
Robert E. Johannes 《Environmental Biology of Fishes》1978,3(1):65-84
Synopsis A synthesis of ethnobiological, behavioral and physical oceanographic information leads to the conclusion that temperate zone models of reproductive strategy are inapplicable to many fishes of the coastal tropics. Intense predation appears to exert heavy selection pressure on fishes that spend their adult lives in coral, mangrove or tropical seagrass communities. Many exhibit spawning behaviors and spawn at times and locations that favor the transport of their pelagic eggs and pelagic larvae offshore where predation is reduced. This creates a countervailing selection pressure — the need to return the larvae to shallow water once they are ready to colonize their post-larval habitats. Accordingly, spawning is often concentrated at times of the year when prevailing winds or currents are at their weakest, thereby reducing the transport of larvae long distances from where they originated. Spawning is also concentrated in the vicinity of nearshore gyres which similarly favor the ultimate return of the larvae to their natal area. Among these species, therefore, offshore larval dispersal does not seem to be an adaptation for dispersal of the species, but rather an evolutionary response to intense predation pressure in the adult habitats. Lunar reproductive periodicity is more common among these species than has previously been recognized, and is one of the strategies employed to enhance the offshore flushing of eggs and larvae.This paper forms part of the proceedings of a mini-symposium convened at Cornell University, Ithaca, N. Y. 18–19 May 1976, entitled Patterns of Community Structure in Fishes (G. S. Helfman, ed.).Contribution No. 524, Hawaii Institute of Marine Biology, University of Hawaii, Honolulu. 相似文献
40.
Conversion of Biovolume Measurements of Soil Organisms, Grown Under Various Moisture Tensions, to Biomass and Their Nutrient Content 总被引:16,自引:10,他引:6 下载免费PDF全文
Direct microscopic measurements of biomass in soil require conversion factors for calculation of the mass of microorganisms from the measured volumes. These factors were determined for two bacteria, five fungi, and a yeast isolated from soil. Moisture stress conditions occurring in nature were simulated by growth in two media using shake cultures, on agar plates, and on membranes held at 34, 330, and 1,390 kPa of suction. The observed conversion factors, i.e., the ratio between dry weight and wet volume, generally increased with increasing moisture stress. The ratios for fungi ranged from 0.11 to 0.41 g/cm3 with an average of 0.33 g/cm3. Correction of earlier data assuming 80% water and a wet-weight specific gravity of 1.1 would require a conversion factor of 1.44. The dry-weight specific gravity of bacteria and yeasts ranged from 0.38 to 1.4 g/cm3 with an average of 0.8 g/cm3. These high values can only occur at 10% ash if no more than 50% of the cell is water, and a specific conversion factor to correct past data for bacterial biomass has not yet been suggested. The high conversion factors for bacteria and yeast could not be explained by shrinkage of cells due to heat fixing, but shrinkage during preparation could not be completely discounted. Moisture stress affected the C, N, and P content of the various organisms, with the ash contents increasing with increasing moisture stress. Although further work is necessary to obtain accurate conversion factors between biovolume and biomass, especially for bacteria, this study clearly indicates that existing data on the specific gravity and the water and nutrient content of microorganisms grown in shake cultures cannot be applied when quantifying the soil microbial biomass. 相似文献