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1.
The discovery that the single p53 gene encodes several different p53 protein isoforms has initiated a flurry of research into the function and regulation of these novel p53 proteins. Full-length p53 protein level is primarily regulated by the E3-ligase Mdm2, which promotes p53 ubiquitination and degradation. Here, we report that all of the novel p53 isoforms are ubiquitinated and degraded to varying degrees in an Mdm2-dependent and -independent manner, and that high-risk human papillomavirus can degrade some but not all of the novel isoforms, demonstrating that full-length p53 and the p53 isoforms are differentially regulated. In addition, we provide the first evidence that Mdm2 promotes the NEDDylation of p53β. Altogether, our data indicates that Mdm2 can distinguish between the p53 isoforms and modify them differently.  相似文献   
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The conformations of the major intermediates trapped during the folding of dendrotoxins I and K from venom of black mamba snakes, have been investigated by circular-dichroism spectroscopy. Local alterations to the native, folded conformations are observed in toxins I and K and in a protein of similar sequence, bovine pancreatic trypsin inhibitor. The inability of intermediates (30-51, 14-38) to complete refolding by forming directly the 5-55 disulphide bond is explained. The following observations on the role of secondary structure in the folding of the three proteins are of interest. 1. It is not necessary for the three proteins to acquire elements of secondary structure at the same stage of folding in order to attain similar three-dimensional conformations. 2. The stability of the final folded state is not directly correlated to an early appearance of secondary structure. 3. The degree of secondary structure already present in intermediates (30-51) seems to determine the pathway of refolding preferred by the corresponding protein.  相似文献   
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Mouse and human cDNA clones encoding the T-cell and mast cell growth factor P40, now designated IL-9, were used to identify DNA restriction fragment length polymorphisms (RFLPs) in sets of somatic cell hybrids and between inbred strains of mice and interspecific backcross progeny. Segregation of mouse and human chromosomes among somatic cell hybrids indicated a location on mouse chromosome 13 and human chromosome 5. RFLPs were identified among inbred strains of mice. Analysis of chromosome 13 alleles for Tcrg, Dhfr, and Il-9 in an interspecific cross between Mus musculus and NFS/N or C58/J mice indicates that IL-9 is distal to Tcrg and Proximal to Dhfr.  相似文献   
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In connectivity models, land cover types are assigned cost values characterizing their resistance to species movements. Landscape genetic methods infer these values from the relationship between genetic differentiation and cost distances. The spatial heterogeneity of population sizes, and consequently genetic drift, is rarely included in this inference although it influences genetic differentiation. Similarly, migration rates and population spatial distributions potentially influence this inference. Here, we assessed the reliability of cost value inference under several migration rates, population spatial patterns and degrees of population size heterogeneity. Additionally, we assessed whether considering intra-population variables, here using gravity models, improved the inference when drift is spatially heterogeneous. We simulated several gene flow intensities between populations with varying local sizes and spatial distributions. We then fit gravity models of genetic distances as a function of (i) the ‘true’ cost distances driving simulations or alternative cost distances, and (ii) intra-population variables (population sizes, patch areas). We determined the conditions making the identification of the ‘true’ costs possible and assessed the contribution of intra-population variables to this objective. Overall, the inference ranked cost scenarios reliably in terms of similarity with the ‘true’ scenario (cost distance Mantel correlations), but this ‘true’ scenario rarely provided the best model goodness of fit. Ranking inaccuracies and failures to identify the ‘true’ scenario were more pronounced when migration was very restricted (<4 dispersal events/generation), population sizes were most heterogeneous and some populations were spatially aggregated. In these situations, considering intra-population variables helps identify cost scenarios reliably, thereby improving cost value inference from genetic data.  相似文献   
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Citrus trees are characterized by a large canopy and low hydraulicconductivity. In Israel's semi-arid summer climate this couldcause transpiration to exceed water uptake and cause temporaryexcessive water deficits. It was hypothesized that reductionof radiative load would reduce transpiration and thus reducedeficits. Net radiation of lemon trees in the hottest season was reducedby shading hedgerows with reflective nets for approximatelyone month in both 1994 and 1995. Stem sap flow and climate variableswere measured continuously. Daily courses of leaf conductanceand leaf water potentials were measured on selected days. Midday net radiation below the dense and sparse shade net treatmentswas 47% and 73% of that above the control trees. Midday ‘sunlit’leaf temperatures below the nets were reduced by 2.7 and 1.6C,respectively. The reduction in net radiation caused large changes in leafconductance. Average midday sunlit leaf conductance measuredin 1995 under the dense and sparse treatments and control were4.1, 2.9 and 1.8mm s–1, respectively (significantly differentat P <0.01). Similar differences in sunlit leaf conductancewere found in 1994. Shade leaf conductance was not affectedby the treatments. Daily total and midday sap flow under the dense net were reducedby 6–7% and 10–11%, respectively. Sap flow underthe sparse net did not change significantly in 1994, but in1995 daily and midday sap flows were reduced by 6% and 7%, respectively.Midday leaf water potentials increased by 0.2 and 0.1 MPa underdense shade in 1994 and 1995, respectively. Under sparse shademidday leaf water potentials increased by 0.1 MPa in 1994, butdid not change significantly in 1995. A modified Penman-Monteith model evaluated transpiration ifleaf conductance were constant in the different radiation environments.At leaf conductance levels found in the unshaded trees, denseshade was estimated to cause a 25% reduction in transpiration,while leaf conductance values found in trees under the denseshade would lead to an increase in transpiration of more than35% in unshaded trees. The ability of the tree to maintain almost constant transpirationin different radiation environments and thus avoid water deficitby adjusting the conductance of sunlit leaves is discussed interms of environmental influences and significance to the plant'swater balance. Key words: Tree transpiration, stomatal closure, climate modification, citrus  相似文献   
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Gradations in cold resistance of plants with different latitudinal and altitudinal distribution, and the various categories of chilling and freezing resistance are hypothesized to be evolutionary steps of adaptive responses to increasing low temperature stress and annual seasonality. The gradual lowering of the critical phase transition temperature of biomembrane lipids, the capacity of persistent supercooling of tissues, and the development of a dormancy linked freezing-tolerance are considered to be essential mechanisms resulting in improved acclimatation to low temperature climates.
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Carbonyl compounds such as alpha-ketoglutarate, pyruvate, oxaloacetate, butyraldehyde, acetaldehyde or acetone react with NAD or NADP to give adducts. Binding studies of adducts to dehydrogenases are performed by means of ultraviolet differential spectroscopy, circular dichroism and spectrofluorimetry. The dehydrogenases show a high degree of binding specificity toward the adducts which contain their specific oxidized substrate and their specific coenzyme. The high selectivity of the dehydrogenases for adducts is evidenced by binding studies of NAD(P)-pyruvate and NAD(P)-alpha-ketoglutarate adducts on glutamate dehydrogenase at pH 7.6 and 8.9. Evidence is presented showing that adducts bind to the active site of the enzymes.  相似文献   
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