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1.
The origin of replication of the IncW plasmid pSa has been cloned and the function of this origin in Escherichia coli examined. A 1.9-kb region of DNA is required for efficient autonomous replication, and a 0.47-kb fragment within this region can initiate replication only in the presence of an autonomously replicating derivative of pSa. An Mr 35,000 protein (repA) is encoded adjacent to the origin and is required for efficient initiation of replication. The derivatives examined provide information suggesting a direct role of partition factors in plasmid replication and incompatibility. 相似文献
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R. C. Close N. T. Moar A. I. Tomlinson A. D. Lowe 《International journal of biometeorology》1978,22(1):1-19
New Zealand lies 2000 km across the Tasman Sea, southeast of Australia, in the path of prevailing westerly winds and thus is well sited for studies of long distance dispersal. The aerial transfer of biological material across the Tasman Sea from Australia to New Zealand is not well documented and evidence for this is reviewed. Plant Pathogens: Regular surveys have identified the races of wheat stem rust present in both countries. In general the identification of a new race in Australia was quickly followed by its appearance in New Zealand. SimilarlyAntirrhinum rust and poplar leaf rusts were detected in New Zealand soon after their first appearance in Australia. Insects: Coccids, the grain aphid, and blue moon and other butterflies and moths appear to have been carried across the Tasman during appropriate meteorological conditions. Seeds and Pollen: There is evidence for a west to east movement of seeds, spores and pollen. The affinities of the orchid and fern floras between the two countries provides circumstantial evidence and it is generally accepted thatCasuarina pollen found in peat and surface samples from various parts of New Zealand has its source in eastern Australia. 相似文献
6.
Isolation and characterization of plasma membrane-associated cortical granules from sea urchin eggs 总被引:9,自引:6,他引:3 下载免费PDF全文
Cortical granules, which are specialized secretory organelles found in ova of many organisms, have been isolated from the eggs of the sea urchins Arbacia punctulata and Strongylocentrtus pupuratus by a simple, rapid procedure. Electron micropscope examination of cortical granules prepared by this procedure reveals that they are tightly attached to large segments of the plasma membrane and its associated vitelline layer. Further evidence that he cortical granules were associated with these cell surface layers was obtained by (125)I-labeling techniques. The cortical granule preparations were found to be rich in proteoesterase, which was purified 32-fold over that detected in a crude homogenate. Similarly, the specific radioactivity of a (125)I-labeled, surface glycoprotein was increased 40-fold. These facts, coupled with electron microscope observations, indicate the isolation procedure yields a preparation in which both the cortical granules and the plasma membrane-vitelline layer are purified to the same extent. Gel electrophoresis of the membrane-associated cortical granule preparation reveals the presence of at least eight polypeptides. The major polypeptide, which is a glycotprotein of apparent mol wt of 100,000, contains most of the radioactivity introduced by (125)I-labeling of the intact eggs. Lysis of the cortical granules is observed under hypotonic conditions, or under isotonic conditions if Ca(2+) ion is present. When lysis is under isotonic conditions is induced by addition of Ca(2+) ion, the electron-dense contents of the granules remain insoluble. In contrast, hypotonic lysis results in release of the contents of the granule in a soluble form. However, in both cases the (125)I-labeled glycoprotein remains insoluble, presumably because it is a component of either the plasma membrane or the vitelline layer. All these findings indicate that, using this purified preparation, it should be possible to carry out in vitro studies to better define some of the initial, surface-related events observed in vivo upon fertilization. 相似文献
7.
Lectin-binding sites on the plasma membranes of rabbit spermatozoa: Changes in surface receptors during epididymal maturation and after ejaculation 总被引:7,自引:5,他引:2 下载免费PDF全文
GL Nicolson N Usui R Yanagimachi H Yanagimachi Smith JR 《The Journal of cell biology》1977,74(3):950-962
Modifications in rabbit sperm plasma membranes during epididymal passage and after ejaculation were investigated by used of three lectins: concanavalin A (Con A); Ricinus communis I (RCA(I)); and wheat germ agglutinin (WGA). During sperm passage from caput to cauda epididymis, agglutination by WGA drastically decreased, and agglutination by RCA(I) slightly decreased, although agglutination by Con A remained approximately unchanged. After ejaculation, spermatozoa were agglutinated to a similar degree or slightly less by Con A, WGA, and RCA(I), compared to cauda epididymal spermatozoa. Ultrastructural examination of sperm lectin-binding sites with ferritin- lectin conjugates revealed differences in the densities of lectin receptors in various sperm regions, and changes in the same regions during epididymal passage and after ejaculation. Ferritin-RCA(I) showed abrupt changes in lectin site densities between acrosomal and postacrosomal regions of sperm heads. The relative amounts of ferritin-RCA(I) bound to heads of caput epididymal or ejaculated spermatozoa. Tail regions were labeled by ferritin RCA(I) almost equally on caput and cauda epididymal spermatozoa, but the middle-piece region of ejaculated spermatozoa was slightly more densely labeled than the principal-piece region, and these two regions on ejaculated spermatozoa were labeled less than on caput and cuada epididymal spermatozoa. Ferritin-WGA densely labeled the acrosomal region of caput epididymal spermatozoa, although labeling of cauda epidiymal spermatozoa was relatively sparse except in the apical area of the acrosomal region. Ejaculated spermatozoa bound only a few molecules of ferritin-WGA, even at the highest conjugate concentrations used. Caput epididymal, but not cauda epididymal or ejaculated spermatozoa, bound ferritin-WGA in the tail regions. Dramatic differences in labeling densities during epididymal passage and after ejaculation were not found with ferritin-Con A. 相似文献
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Ian Close Gareth Shackleton Peter S. Goldfarb G. Gordon Gibson Raj Sharma Doug Howes 《Journal of biochemical and molecular toxicology》1992,7(3):193-198
The influence of both single and concurrent administration of phenobarbital and clofibrate on hepatomegaly, cytochrome P450-depen-dent mixed function oxidase activities, and peroxisome proliferation in male rat liver have been studied. Both xenobiotics separately increase the liver :body weight ratio and their combined administration results in greater hepatomegaly than either compound alone. Both compounds induce NADPH-cytochrome c(P450) reductase activity and laurate ω- and ω-1-hydroxylase activities, but only phenobarbital induces pentoxyresorufin-O-de-alkylase. None of the drug treatments induced microsomal cytochrome b5. Phenobarbital did not cause peroxisome proliferation and inhibited the corresponding clofibrate-dependent proliferation. Taken collectively, our studies have demonstrated that concomitant treatment with phenobarbital and clofibrate are largely permissive with respect to the hepatic mixed function oxidase system but have opposing effects on the phenomenon of peroxisome proliferation in the same tissue. 相似文献
9.
Seasonal patterns of dehydrins and 70-kDa heat-shock proteins in bark tissues of eight species of woody plants 总被引:6,自引:0,他引:6
Michael Wisniewski Timothy J. Close Timothy Artlip Rajeev Arora 《Physiologia plantarum》1996,96(3):496-505
Although considerable effort has been directed at identifying and understanding the function and regulation of stress-induced proteins in herbaceous plants, reports concerning woody plants are limited. Studies with herbaceous crops have revealed similarities in the types of proteins that accumulate in response to a wide array of abiotic stresses and hormonal cues such as the accumulation of abscisic acid. Many of the identified proteins appear to be related to dehydrins (the D-11 subgroup of late-embryogenesis-abundant proteins). The objective of the present study was to determine if seasonal induction of dehydrins is a common feature in woody plants and to see if seasonal patterns existed for other stress-induced proteins. Bark tissues from eight species of woody plants were collected monthly for a period of 1.5 years. The species included: peach (Prunus persica) cv. Loring; apple (Malus domestica) cv. Golden Delicious; thornless blackberry (Rubus sp.) cv. Chester; hybrid poplar (Populus nigra); weeping willow (Salix babylonica); flowering dogwood (Cornus florida); sassafras (Sassafras albidum); and black locust (Robinia pseudo-acacia). Immunoblots of bark proteins were probed with a polyclonal antibody recognizing a conserved region of dehydrin proteins, and monoclonal antibodies directed against members of the HS70 family of heat-shock proteins. Some proteins, immunologically related to dehydrins, appeared to be constitutive; however, distinct seasonal patterns associated with winter acclimation were also observed in all species. The molecular masses of these proteins varied widely, although similarities were observed in related species (willow and poplar). Identification of proteins using the monoclonal antibodies (HSP70, HSC70, BiP) was more definitive because of their inherent specificity, but seasonal patterns were more variable among the eight species examined. This study represents only a precursory examination of several proteins reported to be stress related in herbaceous plants, but the results indicate that these proteins are also common to woody plants and that further research to characterize their regulation and function in relation to stress adaptation and the perennial life cycle of woody plants is warranted. 相似文献
10.
Contraceptive Use and Pregnancy Outcomes among Opioid Drug-Using Women: A Retrospective Cohort Study