The hydrophobic membrane-spanning sequences of the gp52 glycoprotein are required for the pathogenicity of Friend spleen focus-forming virus.

Friend spleen focus-forming virus (SFFV) codes for a transport-defective envelope glycoprotein designated gp52, which is responsible for the leukemogenic properties of the virus. gp52 is a monotopic integral membrane protein anchored in the membrane by a stretch of hydrophobic amino acid residues located near the carboxy terminus of the molecule. We have constructed a mutant SFFV envelope gene in which the sequences that code for the hydrophobic membrane-spanning domain have been deleted, and we expressed this gene by using recombinant vaccinia virus vectors or retroviral vectors. The mutant SFFV envelope gene was found to encode a truncated glycoprotein (gp52t) which was also transport defective; a majority of gp52t remained cell associated, while a small proportion of the molecules underwent oligosaccharide processing. The processed form of gp52t was secreted from the cells. Retroviral vectors carrying the mutant SFFV envelope gene were found to be nonpathogenic in adult mice. These results indicate that the hydrophobic membrane-spanning region of gp52 is required for pathogenicity of SFFV and suggest that these sequences may play a role in signal transduction. The results also indicate that the transport defect of SFFV gp52 is due to structural features of the ectodomain of the molecule.     

Genetic analysis of a lactococcal plasmid replicon

Summary The sequence and genetic organization was determined of the 2508 by lactococcal portion of pFX2, which was derived from a crypticLactococcus lactis subsp.lactis plasmid and used as the basis for construction of a series of lactococcal vectors. A lactococcal plasmid plus origin and two replication protein-coding regions (repA andrepB) were located. RepA has a helix-turn-helix motif, a geometry typical of DNA-binding proteins. RepB shows a high degree of homology to the plasmid replication initiation proteins from other gram-positive bacteria andMycoplasma. The transcribed inverted repeat sequence betweenrepA andrepB could form an attenuator to regulate pFX2 replication. Upstream of theori site, and in a region which was non-essential for replication, a 215 by sequence identical to the staphylococcal plasmid pE194 and carrying the RS_A site was identified. The genetic organization of this lactococcal plasmid replicon shares significant similarity with pE194 group plasmids.     

Changes in pulmonary Cu−Zn contents in superior mesenteric artery occlusion shock of rabbit

Contents of Cu and Zn of into-pulmonary blood (IPB), out-pulmonary blood (OPB), Lung tissue, and supernatant and macrophages of Lung Lavage were determined in superior mesenteric artery occlusion (SMAO) shock of rabbits. Zn of pulmonary tissue was 11.42 +/- 0.60 and 14.52 +/- 1.78 (micrograms/g wet wt) in SMAO shock and control groups, respectively. Content of Zn was found to be lower, Cu was not changed, and Cu/Zn ratio increased in lung tissue in SMAO shock. Contents of Cu and Zn in other samples were not changed. The results suggest that lower Zn in lung tissue related to acute lung injury.     

Mapping of the SLA complex of miniature swine: mapping of the SLA gene complex by pulsed field gel electrophoresis.

The overall order of the regions of the swine major histocompatibility complex (MHC), the SLA complex, was determined by pulsed field gel electrophoresis (PFGE). It was found that the order of the regions is class II-class III-class I. A class I probe hybridized to a 420 kb Mlu I and a 420 kb Not I fragment as did a class III probe for C2. None of the class II probes hybridized to these fragments. Thus, linkage of class I to class III was shown. The class III C2, Bf, and C4 genes were found to residue in a 190 kb Not I fragment. Linkage of class III and class II genes was shown when both the class III C4 and the class II DR probes hybridized to the same 195 kb Sac II and 340 kb Not I fragments. The class I probe did not hybridize to these fragments. The order of the regions, class II-class III-class I, is similar to that of human MHC genes and may have been conserved in evolution so that coordinated expression of MHC genes could be achieved.     

Spatial and temporal localization of FGF receptors in Xenopus laevis

Summary Mesoderm formation is a result of cell-cell interactions between the vegetal and animal hemisphere and is thought to be mediated by inducing peptide growth factors including members of the FGF and TGF superfamilies. Our immunochemical study analyses the distribution of FGF receptors coded by the human flg gene during embryogenesis of Xenopus laevis. Immunostaining was detected in the dorsal and ventral ectoderm and also in the marginal zone of early cleavage, blastula and gastrula stages. Signals were very strong in the mid and late blastula (stage 8 and 9) and declined slightly in the early gastrula (stage 10). A dramatic decrease was observed up to the late gastrula (stage 11⁺). In stage 13 embryos, immunostaining was only found in cells around the blastopore. Isolated ectoderm cultured in vitro showed a similar temporal expression and decrease of the signal as the normal embryos. These results indicate that receptor expression is independent of the interaction of the animal cells with the vegetal part of the embryo. Of interest is the fact that the signal cannot only be found at or near the cell surface but also within the cell. This suggests the presence of an intracellular isoform of the receptor resulting from the endogenous expression of splice variants and the internalization of transmembrane receptor. Taken together our results suggest that the loss of competence (for bFGF around stage 10) is not directly correlated with the presence of receptors. The possible roles of heparan sulphate glucosaminoglycans (low affinity receptors) and control mechanisms in the intracellular signalling pathway downstream of the receptor level should be taken into consideration.     

中国乌头属属下等级数量分类的初步研究

本文取中国乌头属50种(含变种)植物,选取形态学性状46个、化学性状8个、组织学性状5个、生态学性状1个,运用数量分类方法,对该属进行属下等级的分类研究。根据数学分析结果,确定了树系图中变种、种、系、亚属的分级界线,并在聚类分析的基础上,进一步探讨了各等级类群的划分。     

中更新世以来兽类地理分布的变化及其天文气候学的解释

中更新世以来,兽类的地理分布曾发生过重大的变化,如西伯利亚的兽类曾三次大举西迁,入侵西欧.它们分别发生在氧同位素的第16、6、2-4阶段.如果考察过去73万年以来全球所获得的、北半球冬半年平均的太阳辐射量的变化,那么第16、6、2-4阶段乃是太阳辐射量比较低的时期.故中更新世以来兽类地理分布的变化是受气候变迁的制约的.而后者则是受天文因素的自然变化所控制的.     

高原低氧对机体无氧代谢阈值的影响

为了探讨高原低氧对机体无氧代谢阈值(AT)的影响,本研究采用Wasserman无创性方法,分别测定了11名新兵在平原(四川淮口,海拔500m)和经空运进驻高原 (西藏错那,海拔4370m)后的第3、5、7和14天的AT。结果表明:新兵进驻高原后AT由平原的813.6±147.4kg·m/min降低到395.5±194.5 kg·m/min(P<0.01);高原低氧引起AT的降低幅度与受试者平原AT的高低呈正相关(r=0.933,P<0.01);进驻高原后第3、5、7天AT维持在较低水平,随后呈上升趋势。但移居高原1年战士的AT仍低于平原水平(P<0.05)。提示,高原低氧能够显著地降低机体的AT,并且AT越高的个体进驻高原后受低氧环境的影响程度越大。