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61.
62.
The mucus-trap hypothesis on feeding of aquatic nematodes and implications for biodegradation and sediment texture 总被引:2,自引:0,他引:2
Summary Many aquatic nematodes continuously produce with their caudal and pharyngeal glands a slimy trace consisting of sticky, elastic threads which give an acid mucopolysaccharide reaction. Along these traces small particles adhere firmly thus making the traces visible at low magnifications. By creeping repeatedly on their traces the nematodes produce burrows and solid, branched concretions in fine sediments. By these activities soft bottoms acquire a particular framework texture which perhaps may, for instance in the deep sea, enable an interstitial, non-boring microfauna to thrive.The authors suppose that the copious mucus secretion of nematodes is mainly involved in nutrition and they present an hypothesis on the assumed mode of feeding (mucus-trap hypothesis): With their mucus threads these nematodes entrap small detritus particles, bacteria, and macromolecules which subsequently are browsed together with the mucus. The combination of an adhesive mucus thread and the particular mouth construction in nematodes represents a highly elaborated collecting and sorting system for food acquisition. In addition, decomposition processes of organic material coated by the mucus may contribute to a secondary food source which is controlled by nematodes. Feces are embedded within the mucus, and their remaining nutrient content may be subjected to a later re-utilization. 相似文献
63.
64.
The transient electric birefringence of monodisperse oligonucleosomal DNA ranging from 145 to 990 base pairs has been studied. The orientation of fragments can be described in terms of an induced dipole moment with a small contribution of a permanent dipole. The electrical polarizability delta alpha was found to increase linearly with the DNA contour length. This unexpected dependence might result from a bent structure of DNA already considerable for very short segments. The observed delta alpha values agree with a segmental orientation of rigid subunits of length 13-18 nm as estimated in the elastic model of DNA with a kink angle of about 41 degrees. 相似文献
65.
The mendelian inheritance of a human X chromosome-specific DNA sequence polymorphism and its use in linkage studies of genetic disease 总被引:2,自引:0,他引:2
Summary A recombinant DNA sequence, RB6, was isolated from a human X chromosome library and shown to be X-specific by hybridisation to DNA from a human-mouse somatic cell hybrid containing X as the only human chromosome. The cloned sequence was located on the long arm distal to Xq13 using a human-mouse somatic cell hybrid containing a partial human X chromosome. DNA samples isolated from control human females were digested with the restriction enzyme MspI, and analysed by blotting and hybridisation to the radioactive cloned DNA. Eight of 14 individuals from a random population showed a single hybridising band 7.5 kilobase pairs (kb) in length, but six showed an additional band 10.1 kb in length. DNA from 12 members of a family with X-linked thyroxine-binding globulin deficiency was analysed for the segregation of this polymorphism. The results show that the polymorphism is inherited in a Mendelian fashion, and that the disease locus is not closely linked to the polymorphic site. Such polymorphisms will be useful as markers for chromosome mapping and for the antenatal diagnosis of genetic diseases. 相似文献
66.
Inhibitors of proteolytic enzymes were tested for their ability to suppress the clinical signs and CNS lesions produced by injection of purified myelin in complete Freund's adjuvant into Lewis rats. Pepstatin or a series of neutral protease inhibitors including aprotinin, soybean trypsin inhibitor, leupeptin, antipain, transaminomethyl cyclohexane carboxylic acid (AMCA), -amino caproic acid (EACA) nitrophenyl guanidino benzoate (NPGB),d- andl-polylysine, or a new commercial protease inhibitor, dipropionyl Rhein (DPR) were injected daily beginning on day 7 after immunization of rats with myelin. Aprotinin and soybean trypsin inhibitor exacerbated the symptoms and lesions of experimental allergic encephalomyelitis (EAE), leupeptin and antipain had no effect, and the plasminogen activators AMCA, EACA, NPGB, as well as poly-l- and poly-d-lysine and DPR suppressed various aspects of EAE. The measurement of acid protease as a biochemical method for quantitation of the degree of cellular infiltration into the CNS is proposed, and the results with the various treatments presented. AMCA and NPGB may exert their effects at the site of entrance of the lymphoid cells into the CNS. 相似文献
67.
PLC/PRF/5, a tissue culture cell line isolated from a human hepatocellular carcinoma and producing hepatitis B surface antigen, was studied for the presence of hepatitis B virus (HBV)-specific DNA and RNA. PLC/PRF/5 cell DNA accelerated the rate of reassociation of HBV [32P]DNA, and quantitative experiments indicated that the cells contained approximately four copies of viral DNA per haploid, mammalian cell DNA equivalent. PLC/PRF/5 DNA accelerated the rate of reassociation of all individual restriction endonucleases HincII and HaeIII fragments of HBV [32P]DNA, indicating that DNA from all regions of the viral genome is present in the cells. This suggests that these cells contain at least most, and possibly all, of the viral genome. Digestion of PLC/PRF/5 cell DNA with restriction endonuclease HindIII (an enzyme found not to cleave the DNA of any HBV isolate so far examined) yielded only three fragments, all larger than virion DNA, which contained HBV DNA base sequences, suggesting that HBV DNA is integrated in high-molecular-weight DNA at three different sites in these cells and that there is no viral DNA in an episomal form. PLC/PRF/5 cell [32P]RNA was found to hybridize with all restriction fragments of HBV DNA adequately tested, indicating that at least most, and possibly all, of the viral DNA in these cells is transcribed. 相似文献
68.
Summary The purpose of this study is to compare the protein content of parenchymal and non-parenchymal nuclei, as isolated from rat liver. The nucleic have been separated by means of a 1 g-sedimentation technique. The protein content of the separated nuclei has been determined cytophotometrically using the Naphthol Yellow S staining procedure after TCA-extraction (corresponding with the total protein content) and directly (corresponding with the non-histone proteins). The ratio of the total protein content of non-parenchymal, parenchymal diploid and parenchymal tetraploid nuclei respectively was found to be 0.65:1.00:1.90. The ratio of non-histone protein to total protein was the same for all types of nuclei investigated, namely about 55%. 相似文献
69.
70.
Rat liver 60-S ribosomal subunits were submitted to increasing doses of radiation (253.7 nm), at 4 degrees C and 25 degrees C, as previously reported fro 40-S subunits. The existence of protein-RNA cross-linking was demonstrated by two methods. The first consisted in the separation of protein-RNA complex; the second was indirect, and took into account alteration either in the electrophoretic mobility of cross-linked proteins or the separability of 28-S RNA in a 4 M urea/3 M LiCl buffer. The peptide synthetase activity and the sedimentation characteristics of the particles irradiated at 4 degrees C were well preserved, but at 25 degrees C the large subunits were progressively inactivated and unfolded for doses higher than 2 x 10(18) quanta. The dose-dependent variations of protein cross-linkage determined by two-dimensional gel electrophoresis allowed us to distinguish those proteins which reacted at the lowest doses with a first-order reaction from those which cross-linked to RNA after a subtle modification of the subunit structure. At 25 degrees C, all proteins became low-dose reactive. The curve obtained for 28-S RNA cross-linkage was similar to that of the total protein moiety, while those obtained fro the 5-S and 5.8-S RNA (which were parallel) suggest a lower reactivity of these RNAs. As a general rule, proteins from the large subunits were more reactive to RNA than those from the small subunits. This could indicate differences in the organisation of the two subunits. 相似文献