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51.
Understanding the ecological role of species with overlapping distributions is central to inform ecosystem management. Here we describe the diet, trophic level and habitat use of three sympatric stingrays, Hypanus guttatus, H. marianae and H. berthalutzae, through combined stomach content and stable isotope (δ13C and δ15N) analyses. Our integrated approach revealed that H. guttatus is a mesopredator that feeds on a diverse diet of benthic and epibenthic marine and estuarine organisms, principally bivalve molluscs, Alpheus shrimp and teleost fishes. Isotopic data supported movement of this species between marine and estuarine environments. H. berthalutzae is also a marine generalist feeder, but feeds primarily on teleost fishes and cephalopods, and consequently occupies a higher trophic level. In contrast, H. marianae is a mesopredator specialized on shrimps and polychaetas occurring only in the marine environment and occupying a low niche breadth. While niche overlap occurred, the three stingrays utilized the same prey resources at different rates and occupied distinct trophic niches, potentially limiting competition for resources and promoting coexistence. These combined data demonstrate that these three mesopredators perform different ecological roles in the ecosystems they occupy, limiting functional redundancy.  相似文献   
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The small (116 amino acids) inner membrane protein MerT encoded by the transposon Tn501 has been overexpressed under the control of the bacteriophage T7 expression system. Random mutants of MerT were made and screened for loss of mercuric ion hypersensitivity. Several mutantmerT genes were selected and sequenced: Cys24Arg and Cys25Tyr mutations abolish mercury resistance, as do charge-substitution mutations in the first predicted transmembrane helix (Glyl4Arg, Glyl5Arg, Gly27Arg, Ala18Asp), and the termination mutations Trp66Ter and Cys82Ter.  相似文献   
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Abstract: The subtilisin-like prohormone convertase SPC3 is likely to play a role in the biosynthesis of a variety of biologically active peptides. SPC3 undergoes a series of posttranslational processing events during its biosynthesis. Multiple forms have been identified that show varying degrees of truncation at the carboxyl terminus. In this study we show that the 86-kDa form of recombinant SPC3 with an intact carboxyl terminus can undergo rapid carboxyl-terminus truncation to produce a 64-kDa form. We have defined the optimal conditions for carboxyl-terminus truncation in vitro. The carboxyl-terminus truncation reaction was less calcium sensitive, active over a broader pH range, and showed differences in inhibitor sensitivity compared with the enzymatic activities of full-length and truncated forms of SPC3 toward a fluorescent peptide substrate. Increases in enzymatic activity of 86-kDa SPC3 were also measured over a time frame consistent with conversion to the 64-kDa form. However, similar specific activities for both forms of the enzyme suggest such activity increases may not be due to carboxyl-terminus truncation. The different enzymatic properties of the major molecular forms of SPC3 highlight the importance of understanding the molecular events regulating carboxyl-terminal processing of this endoprotease.  相似文献   
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For long-term planning in the delivery of health care, prevalence data are essential for budget estimates in terms both of distribution and training of manpower and fiscal responsibility. From incidence figures, from the knowledge of the natural history of congenital heart disease and from predicted population estimates it is possible to construct a model that reflects the prevalence of congenital heart disease. This has been done for the state of California; the methods used and the data gathered should prove useful nationally.It is estimated that there were in 1975 in California 17,531 children under 21 years of age with congenital heart disease; 24 percent of these had ventricular septal defects and 23 percent had pulmonary stenosis, 11 percent had atrial septal defects and 9 percent had aortic stenosis; the other forms of congenital heart disease constituted the remaining 33 percent. Based on these estimates it is then possible to plan the medical resources necessary for optimal care.  相似文献   
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An improved Enzyme Immunoassay for Myelin Basic Protein is described. Myelin Basic Protein covalently attached to glass balls, and Myelin Basic Protein in samples compete with each other for binding of a peroxidase conjugated anti Myelin Basic Protein antibody. The peroxidase activity on the balls is then inversely proportional to the amount of Myelin Basic Protein in the sample. A detection limit of 0.6 ng/ml is demonstrated for diluent or spinal fluid. For plasma a dilution step increases this to 1.8 ng/ml. Both the coated balls and the peroxidase conjugate are stable for long periods. The assay requires no expensive equipment. Although the assay appears to be valid for subcellular fractions spinal fluid and plasma, successful detection of Myelin Basic Protection peptides in clinical samples may require careful selection of suitable antisera. The assay would be very suitable for eventual use with an appropriate monoclonal antibody.  相似文献   
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Promoter methylation and progressive transgene inactivation inArabidopsis   总被引:1,自引:0,他引:1  
Agrobacterium-transformedArabidopsis plants were generated and the stability of their T-DNA-encoded resistance to kanamycin was examined. Of seven families, each homozygous for a single insertion event, two showed progressive inactivation of resistance over four generations of inbreeding. Loss of resistance was associated with methylation of anSst II site in thenos promoter of the kanamycin resistance gene. Treatment of plant roots from inactive lines with the demethylating agent 5-azacytidine restored the ability of such lines to form callus on kanamycin-containing media. These observations are consistent with the view that methylation is a factor in the progressive inactivation of transgenes inArabidopsis.  相似文献   
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