The occurrence of caulonema-specific proteins in different moss species

Soluble proteins extracted with Tris-buffer pH 8.8 from different mosses are analysed by microgelelectrophoretic method for comparison to the specific proteins present only in the caulonema of Funaria hygrometrica. The protein patterns are also compared with those of liverwort, fern gametophytes and sporophytes and tobacco. It is observed that the caulonema specific proteins are only present in the caulonema of these mosses and are absent in other plants.Abbreviations CSP caulonema specific proteins     

Study on the composition-structure relationship of lipophorins

High density lipophorin (HDLp is the main lipoprotein found in resting insect hemolymph. It has, in general, two molecules of apolipoproteins: apoLp-I (250 kDa) and apoLp-II (80 kDa) and a variable lipid content which ranges from 35% to 59% (w/w). Diacylglycerols (DG), phospholipids (PL), and hydrocarbons (HC) are the main lipid components, whereas cholesterol and triacylglycerols are minor components. DG content varies from 7 to 30%, PL from 11 to 24%, and HC from 0 to 15%. In order to determine the relationship between the lipid composition and the arrangement of lipid and protein components in the lipoprotein particle, a density-composition structural model was designed. The model was established by means of 12 sets of data on lipophorin density-composition relationships, and model validity was determined throughout lipoprotein space- and surface-filling conditions. Despite the differences among the lipid compositions of lipophorins, it is concluded that there are several unifying structural restrictions that govern the molecular organization of lipophorins. Quantitative treatment of the model indicates that lipophorin structure is consistent with the following. 1) Spherical particles with a protein-rich outer layer of approximately 20-21 A thickness, comprised of proteins, phospholipids, cholesterol, and small amounts of DG, and a lipid-rich core composed of HC, TG, and almost all the lipophorin DG. 2) Apolipophorins have a lipid-embedded localization within the lipoprotein particle. They might represent one of the few examples of proteins containing beta-shift structure, exerting strong hydrophobic interaction and having a lipid-embedded localization.(ABSTRACT TRUNCATED AT 250 WORDS)     

Paleolimnology of Qilu Hu,Yunnan Province,China

Qilu Hu is a large (A = 36.9 km²), shallow (z_max = 6.8 m) lake that lies at an elevation of 1797 m above msl on the Yunnan Plateau, southern China. Lake waters are hard (Mg = 3.2m eq L^–1, Ca = 1.3 meq L^–1 ), fresh (conductivity = 380 S cm ^–1), and productive (Secchi < 40 cm). An 11-m sediment core has a basal ¹⁴C age of 30960 ± 860 B.P. Sediments between 11 m and 6 m are high in % dry weight, rich in clay components Al₂O₃, Fe₂O₃, K₂O, MgO, and low in organic C (6.1%), carbonate-C (<1.0%), total N (<3.2 mg g^–1), and total S (<-1.7 mg g^–1). Diatoms and pollen indicate open-water conditions between 9.0 m and 6.0 m (1342011790 B.P.). Above 6.0 m, CaCO₃ and organic matter concentrations increase relative to clastics. The transition marks a change to shallow-water conditions as inferred from diatoms and pollen, and probably reflects a shift to drier climate. Uppermost (80-0 cm) red clays were deposited rapidly, probably as a consequence of recent (decades to centuries) riparian disturbances (e.g. agriculture, lake-bottom reclamation, urban development). Dates assigned to events in the Qilu Hu profile are tentative because of potential hard-water-lake error.     

An efficient method for isolation of plasmid DNA from methylotrophic bacteria

A method, suitable for the isolation of closed circular plasmid DNA from methylotrophic bacteria is described. Improvement of cell lysis was achieved by butanol extraction of cells before application of the lytic agent. Using this method, cryptic plasmids of 7.8, 14, 36 and 200 kb were purified from soil-isolated methylotrophs.     

Heterogeneity of cell surface endothelin receptors

Two distinct cell surface endothelin receptors were identified, namely a 73-kDa protein referred to as ET-R1 and a 60-kDa protein named ET-R2. ET-R1 was expressed as the sole endothelin receptor on rat A10 vascular smooth muscle cells and C6 glial cells. Binding of 125I-ET-1 to these cells was inhibited by 50-200 pM endothelin-1 and -2, whereas endothelin-3 did not compete for this receptor subtype. Binding of 125I-ET-1 to intact A10 and C6 cells was reversible, indicating that ET-R1 is located on the cell surface. Affinity labelling of a single 73-kDa band on sodium dodecyl sulfate-polyacrylamide gels by 125I-ET-1 in A10 and C6 cells was inhibited by endothelin-1 but not by endothelin-3. In A10 cells, endothelin-1 but not endothelin-3 elicited a concentration-dependent increase in intracellular inositol trisphosphate levels. ET-R1 was also expressed in cultured rat glomerular mesangial cells based on findings of a subset of receptors with an apparent molecular mass of 73 kDa that bound 125I-ET-1 displacable by endothelin-1 and endothelin-2 but not by endothelin-3. These cells also expressed the ET-R2 receptor subtype, based on findings of a 60-kDa binding site that could be labeled by both 125I-ET-1 and 125I-ET-3. Labeling of ET-R2 by the radioactive endothelins-1 and -3 was inhibited competitively by endothelins-1, -2, and -3. Furthermore, ET-R2 was shown to be a functional receptor, as endothelin-3 caused inositol trisphosphate levels to rise in mesangial cells. An endothelin binding site with high affinity for endothelin-3 was also identified on rat PC12 pheochromocytoma cells, although the apparent molecular mass of this receptor could not be verified by cross-linking studies. Since endothelin-1 or -3 failed to augment inositol trisphosphate levels in these cells, this binding site could represent a third endothelin receptor subtype. Thus, two distinct functional receptors for endothelins were identified on rat cells, namely the 73-kDa ET-R1 which has an exceedingly low affinity for endothelin-3 and the 60-kDa ET-R2 which binds endothelin-3 with high affinity. Whether an additional endothelin receptor subtype exists in PC12 cells remains to be shown with certainty.     

Discrimination and consistency of five myosin ATPase stains in human normal and duchenne dystrophic muscle

Summary Limitations in the ability of the human visual system to assess accurately the relative staining densities of individual fibers in muscle tissue stained for myosin ATPase can complicate the objective evaluation of fiber type populations. In this study a novel approach is employed which utilizes human visual capabilities to provide accurate fiber classification. Using this approach, the ability of five ATPase staining techniques to discriminate fiber type categories in single samples of human normal and Duchenne dystrophic skeletal muscle is evaluated, as is the consistency of the fiber type classifications between stains. While no major discrepancies in fiber typing were observed in the sample of normal muscle, significant differences in classification, along with a decrease in the ability to discriminate fiber types were noted in the sample of Duchenne muscular dystrophy. For the most part, these discrepancies were resolved by a re-interpretation of the staining characteristics of fibers in one stain.This work was supported in part by NIH grant NS 15584, and by a grant from the Muscular Dystrophy Association     

Site-specific properties of Tn7 transposition into the E. coli Chromosome

Summary A study has been made of the insertional properties of transposon Tn7, a 14 kilobase transposable element encoding resistances to trimethoprim, streptomycin and specitinomycin. It has previously been shown that Tn7 transposes at a low frequency and with low specificity into multiple sites in large transmissible plasmids. However, Tn7 transposes with extrame specificity and at high efficiency into the E. coli chromosome. In all cases we have studied, insertion of Tn7 into the chromosome has occurred at a unique site and with a unique orientation. A combination of genetic and biochemical techniques have been used to precisely locate this site on the E. coli chromosome to minute 82 on the linkage map between markers glmS and uncA.To investigate the nature of this highly specific transpositional event, a small region of the E. coli chromosome that includes the unique site, was cloned into the plasmid vector pBR322. Subsequently a lkb restriction fragment, including the Tn7 insertion site, was sub-cloned from this plasmid into the plasmid pACYC184. We show that Tn7 transposes into both these plasmid recombinants with the frequency and specificity characteristie of the E. coli chromosome.     

Deoxyribonucleic acid relatedness inYersinia enterocolitica andYersinia enterocolitica-like organisms

Yersinia enterocolitica andY. enterocolitica-like strains were characterized by DNA relatedness. These strains formed four distinct DNA relatedness groups: (i) the 5 classical biotypes ofY. enterocolitica sensu stricto as designated by Wauters; (ii) strains that are rhamnose positive and also positive in tests for melibiose, α-methyl-d-glucoside, raffinose, and Simmons' citrate; (iii) strains that are rhamnose positive but negative in tests for melibiose, α-methyl-d-glucoside, and raffinose; (iv) sucrose-negative, Voges-Proskauer-negative, trehalose-positive strains.     

Laser microirradiation of kinetochores in mitotic PtK2 cells

Irradiation of the kinetochore region of PtK₂ chromosomes by laser light of 532 nm was used to study the function of the kinetochore region in chromosome movement and to create artificial micronuclei in cells. When the sister kinetochores of a chromosome were irradiated at prometaphase, the affected chromosome detached from the spindle and exhibited no further directed movements for the duration of mitosis. The chromatids of the chromosome remained attached to one another until anaphase, at which point they separated. No poleward movement of the chromatids was observed, and at telophase they passively moved to one of the daughter cells and were enclosed in a micronucleus. The daughter cell containing the micronucleus was then isolated by micromanipulation and followed through subsequent mitoses. At the next mitosis, two chromosomes, each with two chromatids, condensed in the micronucleus. These chromosomes did not attach to the spindle and showed chromatid separation, but no poleward movements at anaphase. They were again enclosed in micronuclei at telophase. The third generation mitosis was similar to the second. Occasionally, both the irradiation-produced and naturally occurring micronuclei exhibited no chromosome condensation at mitosis. Feulgenstained monolayers of PtK₂ cells with naturally occurring micronuclei showed that some micronuclei stain positive for DNA and others do not. This finding raises questions about the fate of chromosomes in a micronucleus.