Global distribution and conservation of rare and threatened vertebrates

Global conservation strategies commonly assume that different taxonomic groups show congruent geographical patterns of diversity, and that the distribution of extinction-prone species in one group can therefore act as a surrogate for vulnerable species in other groups when conservation decisions are being made. The validity of these assumptions remains unclear, however, because previous tests have been limited in both geographical and taxonomic extent. Here we use a database on the global distribution of 19,349 living bird, mammal and amphibian species to show that, although the distribution of overall species richness is very similar among these groups, congruence in the distribution of rare and threatened species is markedly lower. Congruence is especially low among the very rarest species. Cross-taxon congruence is also highly scale dependent, being particularly low at the finer spatial resolutions relevant to real protected areas. 'Hotspots' of rarity and threat are therefore largely non-overlapping across groups, as are areas chosen to maximize species complementarity. Overall, our results indicate that 'silver-bullet' conservation strategies alone will not deliver efficient conservation solutions. Instead, priority areas for biodiversity conservation must be based on high-resolution data from multiple taxa.     

A mechanical explanation of RNA pseudoknot function in programmed ribosomal frameshifting

The triplet-based genetic code requires that translating ribosomes maintain the reading frame of a messenger RNA faithfully to ensure correct protein synthesis. However, in programmed -1 ribosomal frameshifting, a specific subversion of frame maintenance takes place, wherein the ribosome is forced to shift one nucleotide backwards into an overlapping reading frame and to translate an entirely new sequence of amino acids. This process is indispensable in the replication of numerous viral pathogens, including HIV and the coronavirus associated with severe acute respiratory syndrome, and is also exploited in the expression of several cellular genes. Frameshifting is promoted by an mRNA signal composed of two essential elements: a heptanucleotide 'slippery' sequence and an adjacent mRNA secondary structure, most often an mRNA pseudoknot. How these components operate together to manipulate the ribosome is unknown. Here we describe the observation of a ribosome-mRNA pseudoknot complex that is stalled in the process of -1 frameshifting. Cryoelectron microscopic imaging of purified mammalian 80S ribosomes from rabbit reticulocytes paused at a coronavirus pseudoknot reveals an intermediate of the frameshifting process. From this it can be seen how the pseudoknot interacts with the ribosome to block the mRNA entrance channel, compromising the translocation process and leading to a spring-like deformation of the P-site transfer RNA. In addition, we identify movements of the likely eukaryotic ribosomal helicase and confirm a direct interaction between the translocase eEF2 and the P-site tRNA. Together, the structural changes provide a mechanical explanation of how the pseudoknot manipulates the ribosome into a different reading frame.     

温度和应变率对泡沫镍拉伸行为的影响

研究了泡沫镍分别在四种不同应变率和四种不同温度下的单轴拉伸行为，结果表明：泡沫镍的力学性能(强度和模量)随应变率增大而增大，随温度升高而降低。同时，还给出了泡沫镍的强度和模量随相对密度、温度和应变率变化的表达式。     

Molecular cloning and expression of the major protein kinase C substrate of platelets

In platelets, agonists that stimulate phosphoinositide turnover cause the rapid phosphorylation of a protein of apparent relative molecular mass (Mr) 40-47,000, called P47, by protein kinase C (PKC). Diverse identities have been ascribed to P47 including lipocortin, inositol 1,4,5-trisphosphate 5-phosphomonoesterase, pyruvate dehydrogenase alpha subunit and an actin regulatory protein. We have isolated human P47 clones by immunological screening of a lambda gt11 complementary DNA library from HL-60 cells, a human promyelocytic leukaemia cell line. P47 recombinants thus identified hybridized to a 3.0 kilobase (kb) messenger RNA in mature white blood cell lines; the same mRNA was induced in HL-60 cells during differentiation. A 1,050 base pair (bp) open reading frame that could encode a protein of Mr40,087 was confirmed by comparison with peptide sequences from platelet P47, and by expression of the putative recombinant P47 in E. coli and in vitro. The P47 sequence appears to have been conserved throughout vertebrate evolution, and is not similar to any other known sequence including human lipocortin and the alpha subunit of pyruvate dehydrogenase. The P47 protein contains a potential Ca2+-binding 'EF-hand' structure and a region that strongly resembles known PKC phosphorylation sites.