拟南芥高亲和性K~+转运蛋白AtHAK5功能位点的鉴定

AtHAK5是拟南芥高亲和性钾转运体,其基因表达受低钾条件强烈诱导,编码蛋白在低钾条件下可以整合到质膜.生物信息学分析发现其氨基酸序列含有多处潜在的磷酸化位点.本研究假设这些位点对于AtHAK5的功能至关重要,为探讨AtHAK5的功能位点,分别将AtHAK5 cDNA和带有13种不同点突变位点的AtHAK5转化到athak5突变体中,获得14种稳定表达的转基因植株.利用athak5突变体根对Cs敏感的表型,最终确定T549A和T666A为非核心磷酸化位点.如下11个位点为AtHAK5功能必需位点:F85L,T86A,T311A,T359A,P551S,D552N,S603A,S604A,K668E,S698A和V713L.     

Drug resistance in veterinary helminths

At present, there is no effective alternative to chemical control of parasitic helminths where livestock are grazed intensively. Resistance to anthelmintics has become a major problem in veterinary medicine, and threatens both agricultural income and animal welfare. The molecular and biochemical basis of this resistance is not well understood. The lack of reliable biological and molecular tests means that we are not able to follow the emergence and spread of resistance alleles and clinical resistance as well as we need. This review summarizes some of the recent findings on resistance mechanisms, puts forward some recommendations for limiting its impact and suggests some priorities for research in this area.     

Mapping the Flv locus controlling resistance to flaviviruses on mouse chromosome 5.

Genetically determined resistance to flaviviruses in mice is a dominant trait conferred by alleles at a single autosomal locus designated Flv, but no gene products have been associated with this locus and the mechanism of resistance is not well understood. To further characterize this model of genetic resistance, we conducted mapping studies to determine the chromosomal location of Flv. Because of evidence suggesting that the Flv locus is on chromosome 5, three-point backcross linkage analyses were used to define the location of Flv relative to previously assigned chromosome 5 markers. The results confirm the chromosome 5 location of Flv and indicate a map position between the anchor loci rd and Gus-s. The chromosomal localization of Flv is the first step in the production of a detailed linkage map of the Flv region, which may open approaches to positional cloning of the resistance gene.     

Supramolecular structures of peptide assemblies in membranes by neutron off-plane scattering: method of analysis

In a previous paper (Yang et al., Biophys. J. 75:641-645, 1998), we showed a simple, efficient method of recording the diffraction patterns of supramolecular peptide assemblies in membranes where the samples were prepared in the form of oriented multilayers. Here we develop a method of analysis based on the diffraction theory of two-dimensional liquids. Gramicidin was used as a prototype model because its pore structure in membrane in known. At full hydration, the diffraction patterns of alamethicin and magainin are similar to gramicidin except in the scale of q (the momentum transfer of scattering), clearly indicating that both alamethicin and magainin form pores in membranes but of different sizes. When the hydration of the multilayer samples was decreased while the bilayers were still fluid, the in-plane positions of the membrane pores became correlated from one bilayer to the next. We believe that this is a new manifestation of the hydration force. The effect is most prominent in magainin patterns, which are used to demonstrate the method of analysis. When magainin samples were further dehydrated or cooled, the liquid-like diffraction turned into crystal-like patterns. This discovery points to the possibility of investigating the supramolecular structures with high-order diffraction.     

The binding of closantel to ovine serum albumin, and homogenate fractions of Haemonchus contortus

Closantel binds to the serum proteins of the host and affects blood sucking parasites when they ingest the blood of treated hosts. Closantel binds specifically to ovine serum albumin (K(a) of 9. 3x10(6)M(-1)) at site I, the warfarin/phenylbutazone binding site of albumin Closantel also binds to invertebrate haemocyanin and haemolymph. The strongest binding of closantel in homogenates of H. contortus is found in fractions containing soluble proteins. This binding is of low affinity and, because the site itself is not fully denaturable, it may not be proteinaceous. There is no detectable difference in binding affinity between homogenate fractions from closantel susceptible and resistant isolates of adult or larval worms suggesting that closantel resistance is not due to changes in the closantel receptor or carrier.     

The spatio-temporal colonization and diversification across the Indo-Pacific by a ‘great speciator’ (Aves,Erythropitta erythrogaster)

The Indo-Pacific region has arguably been the most important area for the formulation of theories about biogeography and speciation, but modern studies of the tempo, mode and magnitude of diversification across this region are scarce. We study the biogeographic history and characterize levels of diversification in the wide-ranging passerine bird Erythropitta erythrogaster using molecular, phylogeographic and population genetics methods, as well as morphometric and plumage analyses. Our results suggest that E. erythrogaster colonized the Indo-Pacific during the Pleistocene in an eastward direction following a stepping stone pathway, and that sea-level fluctuations during the Pleistocene may have promoted gene flow only locally. A molecular species delimitation test suggests that several allopatric island populations of E. erythrogaster may be regarded as species. Most of these putative new species are further characterized by diagnostic differences in plumage. Our study reconfirms the E. erythrogaster complex as a ‘great speciator’: it represents a complex of up to 17 allopatrically distributed, reciprocally monophyletic and/or morphologically diagnosable species that originated during the Pleistocene. Our results support the view that observed latitudinal gradients of genetic divergence among avian sister species may have been affected by incomplete knowledge of taxonomic limits in tropical bird species.