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41.
Six naturally occurring but rare alleles of sn-glycerol-3-phosphate dehydrogenase (Gpdh) in Drosophila melanogaster have been investigated in this study. They all belong to a class of Gpdh
UF
(ultra-fast) alleles, because their electrophoretic mobilities are faster than that of the Gpdh
F
(fast) allele. The Gpdh
UF
variants are widespread, and have been reported from five continents. DNA sequence analysis has shown that the change in electrophoretic mobility was in each allele caused by a single amino acid residue substitution in the encoded protein. In the Xiamen
UF
allele it is a substitution of lysine (AAA) to asparagine (AAT) in exon 1 (residue 3). An asparagine (AAT) to aspartate (GAT) change was found in exon 6 (residue 336) in the Iowa
UF
and Netherlands
UF
alleles. The mobility of the Raleigh
UF
allele was altered by a valine (GTG) to glutamate (GAG) substitution in exon 3 (residue 76). Two mutations were detected in the Brazzaville
UF
allele: a lysine (AAG) to methionine (ATG) substitution in exon 2 (residue 68) is responsible for the ultra-fast phenotype of this variant, while a tyrosine (TAT) to phenylalanine (TTT) substitution in exon 4 (residue 244) is not expected to alter the electrophoretic mobility of the encoded protein. These results indicate that the Gpdh
UF
alleles originate from different mutational events, and only two of them — Iowa
UF
and Netherlands
UF
— might share a common ancestry. The GPDH activity of the Iowa
UF
allele is intermediate between those of the Gpdh
S
and Gpdh
F
control stocks. The other Gpdh
UF
variants have lower activities than the controls: Xiamen
UF
-83%, Raleigh
UF
-80% and Brazzaville
UF
-73% of the Gpdh
F
control. 相似文献
42.
S. Laurie Sanderson Catherine R. Chesnutt Phillip S. Lobel 《Environmental Biology of Fishes》1996,46(4):365-373
Synopsis We have quantitatively analyzed a videotape of Seriola dumerili (Carangidae) displaying ram suspension-feeding behavior and ram ventilation in the field. This is the first report of facultative suspension feeding by a piscivorous carangid. The intraoral morphology of S. dumerili is not typical of ram suspension-feeding fishes in that closely-spaced, long gill rakers are lacking. While the mechanism of particle retention is not known for any ram suspension-feeding fish species, scanning electron microscopy revealed denticles on the branchial surfaces of S. dumerili that could play a role in particle entrapment. 相似文献
43.
A temperature-sensitive, protein synthesis-defective mutant ofEscherichia coli exhibiting an altered ribosomal protein L22 has been investigated. The temperature-sensitive mutation was mapped to therplV gene for protein L22. The genes from the wild type and mutant strains were amplified by the polymerase chain reaction and the products were sequenced. A cytosine to thymine transition at position 22 of the coding sequence was found in the mutant DNA, predicting an arginine to cysteine alteration in the protein. A single cysteine residue was found in the isolated mutant protein. This amino acid change accounts for the altered mobility of the mutant protein in two-dimensional gels and during reversed-phase HPLC. The temperature-sensitive phenotype was fully complemented by a plasmid carrying the wild type L22 gene. Ribosomes from the complemented cells showed only wild type protein L22 by two dimensional gel analysis and were as heat-resistant as control ribosomes in a translation assay. The point mutation in the L22 gene is uniquely responsible for the temperature-sensitivity of this strain. 相似文献
44.
The patterns of association of juvenile male and female humpback whales, Megaptera novaeangliae , in the southern Gulf of Maine were studied for evidence of maturational changes. Both males and females became less solitary with age. In males, time spent alone changed from a mean of 55.8% of observations at age one to 26.8% at age six. Females were alone in a mean of 49.9% of observations at age one, but in only 20.5% by age six. However, females that produced calves at five, six or seven were associated with no whales but the calf in 73.8% of observations. Males exhibited a clear age-related trend of increasing associations with adults, notably with adult females which constituted approximately 80% of the associates of males aged six years or more. Females showed a similar trend of increasing associations with adults of both sexes. Tests of association data for whales of known age with similar data for adults of the same sex showed that the association patterns of young males and females became statistically indistinguishable from those of adults by the ages of five and four, respectively. The data suggest that the observed changes in social behaviour are closely linked to the attainment of sexual maturity and preparation for adult roles. The different patterns of males and females after maturity may reflect differing reproductive and life-history strategies. 相似文献
45.
Habitat structure,conspecific presence and spatial variation in the recruitment of a temperate reef fish 总被引:2,自引:0,他引:2
Phillip S. Levin 《Oecologia》1993,94(2):176-185
Pronounced spatial variation in recruitment occurs in many marine invertebrate and fish populations and is thought to be critical to the demography of these species. In this study I examined the importance of habitat structure and the presence of conspecific residents to spatial variation in larval settlement and recruitment in a temperate fish Tautogolabrus adspersus. I define settlement as the movement of individuals from the water column to the benthic habitat, while I refer to recruitment as numbers of individuals surviving some arbitrary period of time after settlement. Experiments in which standard habitats were stocked with conspecifics showed that resident conspecifics were not an important factor contributing to small-scale variability in recruitment. Further correlative analyses demonstrated that large-scale variation in recruitment could not be explained by variability in older age classes. By contrast, manipulations of macroalgal structure within a kelp bed demonstrated that recruitment was significantly higher in habitats with a dense understory of foliose and filamentous algae than in habitats with only crustose algae. Understory algae varied in their pattern of disperison among sites, and the dispersion of fish matched that of the plants. In order to determine the effects of differences in patterns of algal dispersion on the demography of associated T. adspersus populations, I used experimental habitat units to manipulate patterns of dispersion. Settlement was significantly greater to randomly placed versus clumped habitats; however, no differences in recruitment between random and clumped habitats were detected. Because recruitment is a function of the numbers of settlers minus the subsequent loss of settlers, rates of mortality or migration must have been higher in the randomly placed habitats. These results are counter to the current paradigm for reef fishes which suggests that larval settlement is the crucial demographic process producing variability in population abundance. In this experiment patterns of settlement were modified by varying the patch structure of the habitat.Contribution number 278 from the Center for Marine Biology, University of New Hampshire 相似文献
46.
Phillip E. Klebba Jeanette M. Rutz Jun Liu Christopher K. Murphy 《Journal of bioenergetics and biomembranes》1993,25(6):603-611
The recent solution of enteric bacterial porin structure, and new insights into the mechanism by which outer membrane receptor proteins recognize and internalize specific ligands, advocates the re-evaluation of TonB-dependent transport physiology. In this minireview we discuss the potential structural features of siderophore receptors and TonB, and use this analysis to evaluate both existing and new models of energy and signal transduction from the inner membrane to the outer membrane of gram-negative bacteria. 相似文献
47.
Mahmoud A. Hassan Harry Jan Swartz Gordon Inamine Phillip Mullineaux 《Plant Cell, Tissue and Organ Culture》1993,33(1):9-17
Experiments in shoot regeneration and virulentAgrobacterium tumefaciens-mediated transformation were used to develop a protocol forRubus transformation. This protocol was then used to produce transformedRubus plants fromin vitro internodes inoculated with anAgrobacterium tumefaciens encoding neomycin phosphotransferase on its disarmed T-DNA. Two transformed plants were selected from 800 inoculations on a medium containing 10 µg ml–1 kanamycin. Results indicated that this level of kanamycin successfully selected against non-transformed cells but did not reduce the number of transformed, kanamycin-resistant, shoots formed. Enzyme assays and Southern blot analysis verified the presence of the -glucuronidase gene in the plant genome. 相似文献
48.
Use of Fluorinated Compounds To Detect Aromatic Metabolites from m-Cresol in a Methanogenic Consortium: Evidence for a Demethylation Reaction
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Anaerobic sewage sludge was used to enrich a methanogenic m-cresol-degrading consortium. 6-Fluoro-3-methylphenol was synthesized and added to subcultures of the consortium with m-cresol. This caused the accumulation of 4-hydroxy-2-methylbenzoic acid. In a separate experiment, the addition of 3-fluorobenzoic acid caused the transient accumulation of 4-hydroxybenzoic acid. Inhibition with bromoethanesulfonic acid caused the accumulation of benzoic acid. Thus, the proposed degradation pathway was m-cresol → 4-hydroxy-2-methylbenzoic acid → 4-hydroxybenzoic acid → benzoic acid. The m-cresol-degrading consortium was able to convert exogenous 4-hydroxybenzoic acid and benzoic acid to methane. In addition, for each metabolite of m-cresol identified, the corresponding fluorinated metabolite was detected, giving the following sequence: 6-fluoro-3-methylphenol → 5-fluoro-4-hydroxy-2-methylbenzoic acid → 3-fluoro-4-hydroxybenzoic acid → 3-fluorobenzoic acid. The second step in each of these pathways is a novel demethylation which was rate limiting. This demethylation reaction would likely facilitate the transformation of the methyl group to methane, which is consistent with the results of a previous study that showed that the methyl carbon of m-[methyl-14C]cresol was recovered predominantly as [14C]methane (D. J. Roberts, P. M. Fedorak, and S. E. Hrudey, Can. J. Microbiol. 33:335-338, 1987). The final aromatic compound in the proposed route for m-cresol metabolism was benzoic acid, and its detection in these cultures merges the pathway for the methanogenic degradation of m-cresol with those for the anaerobic metabolism of many phenols. 相似文献
49.
John S. Beck Anne E. Kwitek Phillip H. Cogen Andrew K. Metzger Geoffrey M. Duyk Val C. Sheffield 《Human genetics》1993,91(1):25-30
p53 is a tumor suppressor gene located on 17p, a region of the human genome frequently deleted in tumors. Mutation of the p53 gene is an important step leading to development of many forms of human cancer. To simplify the analysis of tumors for p53 point mutations, we describe a GC-clamped denaturing gradient gel assay for detecting single-base substitutions within highly conserved regions of the p53 gene. This assay alows for efficient screening of tumors for single-base substitutions within the p53 gene and can be used to facilitate sequence analysis of p53 point mutations. 相似文献
50.
Phillip W. Berman Gerald R. Nakamura Lavon Riddle Henry Chiu Karen Fisher Mark Champe Alane M. Gray Pamela Ward Sherman Fong 《Journal of cellular biochemistry》1993,52(2):183-195
Full-length (membrane bound) and truncated (secreted) forms of the beta 2 integrin heterodimer, CD11b/CD18 (Mac-1), were expressed in a human kidney cell line (293) that normally does not express leukocyte adhesion molecules (Leu-CAMs). The biosynthesis of recombinant Mac-1 in 293 cells differed from that reported for leukocytes in that heterodimer formation was not required for CD11b to be exported to the cell surface. A stable cell line was constructed that constitutively secreted the recombinant, truncated Mac-1 heterodimer into growth conditioned cell culture medium. A novel monoclonal antibody that enabled an immunoaffinity method for the selective purification of recombinant Mac-1 heterodimers was identified. Sufficient protein was purified to allow the first measurement of the 50% inhibitory concentration (IC50) for CD11b/CD18 and for the direct comparison of the inhibitory activity of recombinant soluble Mac-1 with that of various CD18 and CD11b specific monoclonal antibodies. Purified recombinant soluble Mac-1 inhibited the binding of neutrophils, activated by opsonized zymosan or fMet-Leu-Phe peptide, to human umbilical vein endothelial cells. Similarly, the recombinant integrin was effective in inhibiting the binding of unactivated neutrophils to tumor necrosis factor (TNF-alpha) activated endothelial cells. The availability of an abundant source of purified, biologically active Mac-1 will enable direct physical and chemical investigations into the relationship between the structure and function of this leukocyte adhesion molecule. 相似文献