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21.
Christina Lyra Harri Savilahti Dennis H. Bamford 《Molecular & general genetics : MGG》1991,228(1-2):65-69
Summary Using electroporation with the phage PRD1 genome, we set up a high-frequency DNA transfer system for a linear dsDNA molecule with 5-covalently linked terminal proteins. The transfer was saturated when more than 100 ng of PRD1 genome was used. Electroporation efficiency was about four orders of magnitude higher than that obtained with transfection. Removal of the terminal protein abolished plaque formation, which could not be rescued by supplying the terminal protein or phage DNA polymerase or both in trans. 相似文献
22.
The maturation of zygotes formed by the fusion of two gametes is the essential part of the diploid phase of the Chlamydomonas reinhardtii sexual life cycle and results in mature zygotes competent to germinate. To understand the molecular mechanisms underlying zygote maturation and the attainment of competence for germination we isolated genomic clones representing three different genes that are specifically expressed in Chlamydomonas reinhardtii zygotes. Accumulation of the RNAs started more than 24 h after mating, setting these genes apart from genes expressed in young zygotes [9]. Upon light-induced germination of zygotes, the mRNAs disappeared. The patterns of RNA accumulation and disappearance were gene-specific and suggested a function of these genes in maturation and/or in initial steps of germination. 相似文献
23.
24.
Christina Skarpe 《Plant Ecology》1986,68(1):3-18
Sixteen vegetation types were described from a north-south transect in the western Kalahari. Pronounced differences were found between communities on the nutrient poor red Kalahari sand, covering most of the area and those on fine soils and white calcareous sand. Syntaxa resulting from severe overgrazing by livestock were in most cases clearly distinguished from the less disturbed vegetation. The communities on red sand consisted mainly of shrub savanna dominated by perennial tufted grasses, whereas in the vegetation on calcareous material and on overgrazed land, forbs, dwarf shrubs and shrubs played a more important role. The major communities on red sand showed a clear geographical zonation roughly corresponding to the gradient in mean annual rainfall and its interannual variation. In the northern and central Kalahari these syntaxa were dominated by species of Sudano-Zambezian origin and in the southern Kalahari by species showing Karoo-Namib affinities. 相似文献
25.
26.
Christina Scharnhorst Hartmut Heinze Gabriele Meyer Waldemar Kolanus Klaus Bartsch Susanne Heinrichs Thomas Gudschun Margret Möller Frank Herzfeld 《Plant molecular biology》1985,4(4):241-245
Summary cDNA clones were isolated for a chloroplast protein, the mRNA of which is induced to maximum levels within 2–4 h after onset
of illumination in five day old, etiolated pea seedlings.
The cDNA library was constructed from poly(A)+-mRNA which was isolated from 4 h illuminated seedlings. The extremely short induction period of the early light induced protein(ELIP)-mRNA
established the basis of our screening procedure. Colony hybridization experiments were performed with32P-labelled cDNA probes, synthesized from RNA of seedlings which had been exposed to different programs of illumination. Plasmid
DNAs were isolated from colonies showing strong hybridization signals exclusively with cDNA corresponding to the 4 h-mRNA.
Hybrid released translation of preselected plasmids p 17/C2 and p17/C4 revealed a peptide of Mr 24 000. After posttranslational importin vitro, the processed product of Mr 17 000 appears in the chloroplast. Using these clones, the expression of the ELIP-mRNA was investigated by DOT-hybridization.
The ELIP-mRNA reaches maximum levels within 2–4 hours after onset of illumination. Our results correspond precisely to thein vivo characteristics and indicate positive identification of the sought clones. 相似文献
27.
Summary Thin sections of budding yeast cells and giant gells grown after X-irradiation have been examined by electron microscopy. The different steps of cross-wall formation during budding were documented with unirradiated cells. With X-ray induced giant cells cytokinesis was shown to be absent. Neither primary nor secondary septae appeared thus cell separation did not occur. Despite this fact both macromolecular synthesis and bud growth continued, giving rise to the formation of giant cells. 相似文献
28.
W A Wegener 《Biophysical journal》1984,46(6):795-803
Pump-and-probe techniques can be used to follow the slow rotational motions of fluorescent labels bound to macromolecules in solution. A strong pulse of polarized light initially anisotropically depletes the ground-state population. A continuous low-intensity beam of variable polarization then probes the anisotropic ground-state distribution. Using an additional emission polarizer, the generated fluorescence can be recorded as it rises towards its prepump value. A general theory of fluorescence recovery spectroscopy (FRS) is presented that allows for irreversible depletion processes like photobleaching as well as slowly reversible processes like triplet formation. In either case, rotational motions modulate recovery through cosine-squared laws for dipolar absorption and emission processes. Certain pump, probe, and emission polarization directions eliminate the directional dependence of either dipole and simplify the resulting expressions. Two anisotropy functions can then be constructed to independently monitor the rotations of either dipole. These functions are identical in form to the anisotropy used in fluorescence depolarization measurements and all rotational models developed there apply here with minor modifications. Several setups are discussed that achieve the necessary polarization alignments. These include right-angle detection equipment that is commonly available in laboratories using fluorescence methods. 相似文献
29.
Genes for human U4 small nuclear RNA 总被引:10,自引:0,他引:10
30.
Some properties of monolayers of (POPG) alone or of POPG in mixtures with (DPPC) have been measured near 35°C during dynamic compression and expansion at 3.6 cm2·s?1. (2) The mean values of minimum surface tension (corresponding to maximum surface pressure) which could be obtained with pure POPG monolayers at high compression ranged from 15 to 18 mN·m?1 in the presence of Na+, Ca2+ or low pH (2.0) in the subphase. (3) The presence of Ca2+ or low pH in the subphase increased the collapse plateau ratios obtained on cyclic compression. This might represent enhanced respreading into the monolayer of pure POPG from a collapsed form during reexpansion of the surface. (4) Monolayers containing 10% or 30% POPG and 90% or 70% DPPC could be compressed to surface tensions approaching zero. (5) In such mixed monolayers, 10% or 30% POPG did not appear to enhance respreading, as measured by collapse plateau ratios, in the presence of Na+ or Ca2+ in the subphase. 相似文献