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41.
Begonia (sect.Gireoudia)lyman-smithii is described and illustrated, and its relationships are discussed. 相似文献
42.
43.
Studies of Río Negro subsistence farming and fishing activities are used to estimate the human carrying capacity for the region and the likely pattern of human land-use during prehistory. Ceramic evidence suggests human presence in the region more than 3000 years ago. Traditional farming is labor intensive and relatively unproductive. Nevertheless, farmers achieve an energy return of 15.21, and produce 2600 kcal per work hour. Fish are the major protein source, but fish catch per unit of effort and fish yield per hectare of floodplain are very low; fishermen are probably exploiting local fish resources very close to their limit. The low human population density would suggest that the Río Negro forest has been relatively undisturbed. Nevertheless, charcoal is widespread and abundant in forest soils. This charcoal is probably from anthropogenic or natural wildfires. These results suggest a much more complex history for Amazonia than previously thought.K. Clark is a free-lance biologist residing in Lima, Peru 相似文献
44.
Abstract The genomes of DNA phage ΦX174 and of RNA phage MS2 each encode a single lysis protein, E protein and L protein, respectively. Based on the known DNA and protein sequences, and with the aid of structural predictions of the proteins, a chimeric gene was constructed. The resulting protein was composed of the N-terminal sequence of E protein and the C-terminal sequence of L protein. The truncated E and L polypeptides used in this construction were functionally inactive. However, the chimeric gene product had very high lysis-inducing activity. This construction is an example which could be extended to the engineering of other lysis proteins designed with specific biotechnological processes in mind. 相似文献
45.
Summary A DNA deletion in a patient with Becker muscular dystrophy (BMD) has been delineated by restriction endonuclease mapping. The deletion is unusually small, removing six kilobases (kb) of DNA distal to pERT 87-1 (DXS164). This region has previously been shown to contain an exon of a candidate gene which, when defective, causes Duchenne muscular dystrophy (DMD) or Becker muscular dystrophy. Removal of this exon and surrounding DNA is apparently sufficient, in this case, to cause a BMD phenotype. The occurrence of this deletion in DXS164 would appear to confirm that this region is part of the BMD locus. Many DMD patients have deletions in and around this region, adding further evidence for the allelic nature of the two disorders. This fortuitous deletion may identify a functionally important domain of the protein product in terms of the severity of phenotype manifested. 相似文献
46.
47.
Aminoglycoside suppression at UAG, UAA and UGA codons in Escherichia coli and human tissue culture cells 总被引:6,自引:0,他引:6
Robin Martin Anne E. Mogg Louise A. Heywood Lars Nitschke Julian F. Burke 《Molecular & general genetics : MGG》1989,217(2-3):411-418
Summary We have compared the suppression of nonsense mutations by aminoglycoside antibiotics inEscherichia coli and in human 293 cells. Six nonsense alleles of the chloramphenicol acetyl transferase (cat) gene, in the vector pRSVcat, were suppressed by growth in G418 and paromomycin. Readthrough at UAG, UAA and UGA codons was monitored with enzyme assays
for chloramphenicol acetyl transferase (CAT), in stably transformed bacteria and during transient expression from the same
plasmid in human 293 tissue culture cells. We have found significant differences in the degree of suppression amongst three
UAG codons and two UAA codons in different mRNA contexts. However, the pattern of these effects are not the same in the two
organisms. Our data suggest that context effects of nonsense suppression may operate under different rules inE. coli and human cells. 相似文献
48.
Anin situ method, derived from anin vivo method, was used to determine nitrate reductase activity (NRA) in:i) excised barley and corn shoots and excised soybean leaves
during a N-depletion experiment and; ii) roots and shoots of N-depleted barley and corn seedlings during induction of nitrate,
reductase (NR). Nitrate reduction, calculated from thesein situ RNA measurements, was compared with estimates of each organ's nitrate reduction in light aerobic conditions from NO
3
−
consumption and a15N model (Gojonet al., 1986b).
Thein situ RNA of roots strongly underestimated their15NO
3
−
reduction. In contrast, in barley and corn shoots and in the first trifoliolate leaves from 26-day-old, soybean, thein situ NRA assay gave a fair approximation of the true NO
3
−
reduction rate (relative differences ranging from −14 to +32%). In young soybean leaves (from 20-day-old plants), however,
thein situ NRA strongly underestimated the actual NO
3
−
reduction. The physiological significance of thein situ NRA assay in shoots and roots, and its value for field studies are discussed from these results. 相似文献
49.
Komandoor E. Achyuthan Ann Mary Robin Bhaermani Charles S. Greenberg 《Molecular and cellular biochemistry》1989,85(1):57-65
Calcium ions are crucial for expression of transglutaminase activity. Although lanthanides have been reported to substitute for calcium in a variety of protein functions, they did not replace the calcium requirement during transglutaminase activity measurements. Furthermore, lanthanides strongly inhibited purified liver transglutaminase activity using either casein or fibrinogen as substrates. Terbium (III) inhibition of transglutaminase-catalyzed putrescine incorporation into casein was not reversed by the presence of 10–200 fold molar excess of calcium ions (Ki for Tb(III)=60 µM). Conformational changes in purified liver transglutaminase upon Tb(III) binding were evident from a biphasic effect of Tb(III) on transglutaminase binding to fibrin. Low concentrations of Tb(III) (1 µM to 10 µM inhibited the binding of transglutaminase to fibrin, whereas higher concentrations (20 µM to 100 µM promoted binding. Conformational changes in purified liver transglutaminase consequent to Tb(III) binding were also demonstrated by fluorescence spectroscopy due to Forster energy transfer. Fluorescence emission was stable to the presence of 200 mM NaCl and 100 mM CaCl2 only partially quenched emission. Purified liver transglutaminase strongly bound to Tb(III)-Chelating Sepharose beads and binding could not be disrupted by 100 mM CaCl2 solution. Our data suggest that Tb(III)-induced conformational changes in transglutaminase are responsible for the observed effects on enzyme structure and function. The potential applications of Tb(III)-transglutaminase interactions in elucidating the structure-function relationships of liver transglutaminase are discussed. 相似文献
50.
The glue protein of ribbed mussels (Geukensia demissa): a natural adhesive with some features of collagen 总被引:1,自引:0,他引:1
J. Herbert Waite Douglas C. Hansen Kathleen T. Little 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(5):517-525
Summary The Atlantic ribbed musselGeukensia (Modiolus)demissa attaches itself to the roots of cord grass and other hard objects in tidal salt marshes by spinning adhesive byssal threads. The precursor of a protein apparently present in the adhesive plaques of the threads was isolated in quantity from the foot of the mussel. The protein has an apparent molecular weight of 130000, a pI of 8.1, and contains a high proportion of Gly, Glu/Gln, Lys and 3,4-dihydroxyphenyl-l-alanine (DOPA). Sequence of tryptic peptides suggests a pattern of repeated motifs, such as: Gly-DOPA-Lys, and X-Gly-DOPA-Y-Z-Gly-DOPA/Tyr-Lys, where X is Thr or Ala in octapeptides and Gln-Thr in nonapeptides. Y is variable, but more often than not hydrophobic; and Z is frequently Pro or 4-trans-hydroxyproline (Hyp). The presence of Pro-Gly and Hyp-Gly sequences of -hydroxylysine in the protein is reminiscent of typical collagens; however, the protein is not labile to clostridial collagenase, nor does collagen cross-react with antibodies raised against the mussel protein. Unlike typical collagens, Gly probably occurs only at every 4th or 5th residue in this unusual mussel protein.Abbreviations
Anti-Gdfp
anti-G. demissa foot protein
-
Dopa
3,4-dihydroxyphenylalanine
-
CTAB
cetyltrimethylammonium bromide
-
HPLC
high performance liquid chromatography
-
PAGE
polyacrylamide gel electrophoresis
Supported by grants from the National Science Foundation (DMB 8500301) and the Office of Naval Research (N00014-86K-0717) 相似文献