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11.
A budding coccoid bacterium, (CH1), a Vibrio sp. and a Pseudomonas sp. were investigated for factors governing their attachment to glass surfaces in static batch culture and laminar flow continuous culture systems. An analysis of variance showed that the three species exhibited very different responses. For CH1 attachment was dependent on cell density, incubation time and nutrient concentration. The Vibrio sp. was affected by nutrient concentration while the attachment of the Pseudomonas sp. was independent of cell density, incubation time and nutrient concentration. A comparison of attachment to hydrophilic and hydrophobic surfaces showed that attachment of the Vibrio sp. and CH1 to hydrophilic surfaces was 3 and 10 times greater respectively than to hydrophobic surfaces while Pseudomonas attached in equal numbers to both surfaces. The continuous culture system with defined flow hydrodynamics and growth conditions at steady state revealed a random sampling effect 3 times smaller than the batch culture system did. When the biofilm development of Pseudomonas sp. was followed during 46 h at different fluid shear under laminar and turbulent flow conditions, the former biofilm reached 3.3·108 cells·cm-2 and the latter 8.2·107 cells·cm-2.Non-common abbreviation NSS Nine salt solution  相似文献   
12.
Male and female Aedes aegypti (L.) mosquitoes of the laboratory strain ROCK were irradiated with 130 mw of argon 514.5 nm laser microbeams for 0.04, 0.25, 0.4, and 0.5 s, respectively. Egg production, percentage hatch, and productivity (average number of adults surviving after 3 wk) were used to assess mutagenic effects. Mortality was high for males in all laser radiation groups and increased with time of exposure. Except for the group treated for 0.25 s, significant reductions in total F1 progeny also were demonstrated for all other experimentals when male parents were exposed to laser radiation. Females showed a high mortality when subjected to 0.4- and 0.5-s laser radiation. No F1 progeny were produced when parental females were exposed for 0.25, 0.4, and 0.5 s. Numbers of F1 progeny from females exposed to 0.04 s of laser radiation were significantly reduced. A comparison of weekly mean number of progeny showed that the important differences in productivity occurred during the first and second week, respectively, when either male or female adult parents were subjected to laser radiation.  相似文献   
13.
The ability of series of U1 snRNAs and U6 snRNAs to migrate into the nucleus of Xenopus oocytes after injection into the cytoplasm was analyzed. The U snRNAs were made either by injecting U snRNA genes into the nucleus of oocytes or, synthetically, by T7 RNA polymerase, incorporating a variety of cap structures. The results indicate that nuclear targeting of U1 snRNA requires both a trimethylguanosine cap structure and binding of at least one common U snRNP protein. Using synthetic U6 snRNAs, it is further demonstrated that the trimethylguanosine cap structure can act in nuclear targeting in the absence of the common U snRNP proteins. These results imply that U snRNP nuclear targeting signals are of a modular nature.  相似文献   
14.
Monomethylated cap structures facilitate RNA export from the nucleus   总被引:71,自引:0,他引:71  
J Hamm  I W Mattaj 《Cell》1990,63(1):109-118
RNA export from the nucleus has been analyzed in Xenopus oocytes. U1 snRNAs made by RNA polymerase II were exported into the cytoplasm, while U1 snRNAs synthesized by RNA polymerase III, and therefore with a different cap structure, remained in the nucleus. Export of the polymerase II-transcribed RNAs was inhibited by the cap analog m7GpppG. Spliced mRNAs carrying monomethylguanosine cap structures were rapidly exported, while hypermethylated cap structures delayed mRNA export. The export of a mutant precursor mRNA unable to form detectable splicing complexes was also significantly delayed by incorporation of a hypermethylated cap structure. The results suggest that the m7GpppN cap structure is likely to be a signal for RNA export from the nucleus.  相似文献   
15.
We developed a noninvasive rapid fluorimetric method for the investigation of growth of adhering (benthic) phototrophic microorganisms. The technique is based on the sensitive detection of the in vivo fluorescence of chlorophylls chlorophyll a and bacteriochlorophyll a and monitors increases in signal over time as an indicator for growth. The growth fluorimeter uses modulated excitation light of blue-light-emitting diodes and a photodiode as the detector. The light-emitting diodes are mounted geometrically in an aluminum housing for efficient and uniform illumination of the bottoms of the growth containers. The fluorimeter was characterized with respect to detection limit and dynamic range. This system is capable of resolving in vivo chlorophyll a concentrations of 0.5 (mu)g liter(sup-1) in cyanobacteria and 0.03 (mu)g liter(sup-1) in diatoms as well as in vivo bacteriochlorophyll a concentrations in phototrophic bacteria of 0.3 (mu)g liter(sup-1), which points to an extremely high sensitivity compared with that of similar available techniques. Thus, the new fluorimeter allows the determination of growth at extremely low cell densities. The instrument was used successfully to measure the growth of several adhering isolates of the filamentous cyanobacterium Microcoleus chthonoplastes from benthic microbial mats in seawater of different salinities. The data obtained demonstrate broad growth responses for all strains, which thus can be characterized as euryhaline organisms.  相似文献   
16.
A simple and versatile method of in vitro site-specific mutagenesis based on polymerase chain reaction (PCR) is described. The complete method required the use of three oligonucleotide primers and two PCRs. The product of the first PCR was used as one of the primers (megaprimer) in the second PCR. Essentially 100% of the final product incorporated the desired mutation. The various aspects of the procedure and its application is described in detail.  相似文献   
17.
Abstract. Normal (non-transformed) human mammary epithelial cell lines derived from reduction mammoplasties were analyzed by immunocytochemistry with more than 80 monoclonal antibodies (mAbs) and other specific reagents to tissue-specific and developmentally regulated antigens at different passage levels. A subpopulation of poorly differentiated, proliferating epithelial cells, corresponding to the 'selected' cell type of late passages, is shown to be characterized by a new marker, the histo-blood group antigen H type 2, probably carried on a membrane-bound glycolipid. These cells also express a number of other onco-developmental carbohydrate antigens [Ley, Lex, sialosyl-Lea, precursor of Thomsen Friedenreich antigen (Tn), but not Thomsen-Friedenreich antigen and sialosyl-Tn]. Their cytokeratin (CK) phenotype, as assessed by reactivity with monospecific mAbs and two-dimensional gel electrophoresis, is CK 5, 6, 14 and 17, with CK 19 being consistently absent, and varying minor amounts of CK 7, 8 and 18, as well as 15 and 16. The reactivity of these cells with a panel of 11 mAbs specific for CK 18 varies considerably even after cloning, indicating heterogeneity of epitope expression or accessibility. Our data strongly suggest that the H type 2+ cells develop from the basal cell layer of the mammary gland.  相似文献   
18.
    
The limited proteolytic pattern of transducin,G t , and its purified subunits with chymotrypsin were analyzed and the cleavage sites on the t subunit were identified. The t subunit in the GTPS bound form was cleaved into a major 38 kD fragment, whereas t -GDP was progressively digested into 38, 23, 21, and 15 kD fragments. The t subunit was not very sensitive to proteolytic digestion with chymotrypsin. The t subunit was not cleaved and only a small portion of t was digested into several fragments. In order to determine which proteolytic fragment of t still contained the carboxyl terminal region, chymotrypsinization was carried out usingG t previously32P-labeled at Cys347 by petrussis toxin-catalyzed ADP-ribosylation. The32P-label was mainly associated with the t subunit and a 15 kD fragment. The 23 and 21 kD fragments were not32P-labeled. Analysis of amino terminal sequences of 38, 21, and 15 kD proteolytic bands allowed the identification of the major cleavage sites. Chymotrypsin had two cleavage sites in the amino terminal region of t , at Leu15 and Leu19. Chymotrypsin removed 15–19 amino acid residues from the amino terminus of t , generating two peptides (38 kD) which comigrates in gel electrophoresis. Chymotrypsin also cleaved at Trp207 in a conformation-dependent manner. Trp207 of t -GTPS was resistant to proteolysis but t -GDP and the 38 kD fragments of t -GDP produced the 23 and 21 kD fragments, respectively, and a 15 kD fragment containing the carboxyl terminus. This proves that the environment of Trp207 changes when GTP or GTPS is bound, leading to its inaccessibility to chymotrypsin.  相似文献   
19.
Peptide purification by high-performance liquid chromatography (HPLC) is associated with high solvent consumption, relatively large effort and lack of efficient parallelization. As an alternative, many catch-and-release (c&r) purification methods have been developed over the last decades to enable the efficient parallel purification of peptides originating from solid-phase peptide synthesis (SPPS). However, with one exception, none of the c&r systems has been widely established in industry and academia until today. Herein, we present an entirely new chromatography-free purification concept for peptides synthesized on a solid support, termed reactive capping purification (RCP). The RCP method relies on the capping of truncation peptides arising from incomplete coupling of amino acids during SPPS with a reactive tag. The reactive tag contains a masked functionality that, upon liberation during cleavage from the resin, enables straightforward purification of the peptide by incubation with a resin-bound reactive moiety. In this work, two different reactive tags based on masked thiols were developed. Capping with these reactive tags during SPPS led to effective modification of truncated sequences and subsequent removal of the latter by chemoselective reaction with a maleimide-functionalized solid support. By introducing a suitable protecting group strategy, the thiol-based RCP method described here could also be successfully applied to a thiol-containing peptide. Finally, the purification of a 15-meric peptide by the RCP method was demonstrated. The developed method has low solvent consumption, has the potential for efficient parallelization, uses readily available reagents, and is experimentally simple to perform.  相似文献   
20.
Coastal kelp forests produce substantial marine carbon due to high annual net primary production (NPP) rates, but upscaling of NPP estimates over time and space remains difficult. We investigated the impact of variable underwater photosynthetically active radiation (PAR) and photosynthetic parameters on photosynthetic oxygen production of Laminaria hyperborea, the dominant NE-Atlantic kelp species, throughout summer 2014. Collection depth of kelp had no effect on chlorophyll a content, pointing to a high photoacclimation potential of L. hyperborea towards incident light. However, chlorophyll a and photosynthesis versus irradiance parameters differed significantly along the blade gradient when normalized to fresh mass, potentially introducing large uncertainties in NPP upscaling to whole thalli. Therefore, we recommend a normalization to kelp tissue area, which is stable over the blade gradient. Continuous PAR measurements revealed a highly variable underwater light climate at our study site (Helgoland, North Sea) in summer 2014, reflected by PAR attenuation coefficients (Kd) between 0.28 and 0.87 m−1. Our data highlight the importance of continuous underwater light measurements or representative average values using a weighted Kd to account for large PAR variability in NPP calculations. Strong winds in August increased turbidity, resulting in a negative carbon balance at depths >3–4 m over several weeks, considerably impacting kelp productivity. Estimated daily summer NPP over all four depths was 1.48 ± 0.97 g C · m−2 seafloor · d−1 for the Helgolandic kelp forest, which is in the range of other kelp forests along European coastlines.  相似文献   
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