Mutations in the matrix protein of human immunodeficiency virus type 1 inhibit surface expression and virion incorporation of viral envelope glycoproteins in CD4+ T lymphocytes.

Highly conserved amino acids in the second helix structure of the human immunodeficiency virus type 1 (HIV-1) MA protein were identified to be critical for the incorporation of viral Env proteins into HIV-1 virions from transfected COS-7 cells. The effects of these MA mutations on viral replication in the HIV-1 natural target cells, CD4+ T lymphocytes, were evaluated by using a newly developed system. In CD4+ T lymphocytes, mutations in the MA domain of HIV-1 Gag also inhibited the incorporation of viral Env proteins into mature HIV-1 virions. Furthermore, mutations in the MA domain of HIV-1 Gag reduced surface expression of viral Env proteins in CD4+ T lymphocytes. The synthesis of gp160 and cleavage of gp160 to gp120 were not significantly affected by MA mutations. On the other hand, the stability of gp120 in MA mutant-infected cells was significantly reduced compared to that in the parental wild-type virus-infected cells. These results suggest that functional interaction between HIV-1 Gag and Env proteins is not only critical for efficient incorporation of Env proteins into mature virions but also important for proper intracellular transport and stable surface expression of viral Env proteins in infected CD4+ T lymphocytes. A single amino acid substitution in MA abolished virus infectivity in dividing CD4+ T lymphocytes without significantly affecting virus assembly, virus release, or incorporation of Gag-Pol and Env proteins, suggesting that in addition to its functional role in virus assembly, the MA protein of HIV-1 also plays an important role in other steps of virus replication.     

Esophageal PCO2 as a monitor of perfusion failure during hemorrhagic shock

Sato, Yoji, Max Harry Weil, Wanchun Tang, Shijie Sun,Jianlin Xie, Joe Bisera, and Hidehiro Hosaka. EsophagealPCO₂ as a monitor of perfusionfailure during hemorrhagic shock. J. Appl.Physiol. 82(2): 558-562, 1997.Measurement ofgastric wall PCO₂(Pg_CO2) bytonometric method has emerged as an attractive option for estimatingvisceral perfusion during circulatory shock. However, gastric acidsecretion obfuscates the tonometric measurement. We, therefore,investigated the option of measuringPCO₂ in the esophagus to minimizethese restraints. Hemorrhagic shock was induced in five Sprague-Dawleyrats, and five rats served as sham controls.Pg_CO2 wasmeasured with an ion-sensitive field effect transistor that wassurgically implanted into the gastric wall. Esophageal luminalPCO₂(Pe_CO2) wasmeasured by a second ion-sensitive field effect transistor sensor.During hemorrhagic shock, mean aortic pressure declined from 150 to 50 mmHg. Gastric blood flow decreased from 58 to 12 ml ^· min^{1 ·} 100 g¹ (21% of preshock) andesophageal blood flow from 44 to 7 ml ^· min^{1 ·} 100 g¹ (16% of preshock).Pg_CO2simultaneously increased from 47 to 116 Torr andPe_CO2 from 47 to 127 Torr. The increases inPg_CO2 werehighly correlated with increases inPe_CO2(r = 0.90). Esophageal tonometry may,therefore, serve as a practical alternative to gastric tonometry.

     

抗杀螟硫磷二化螟的抗性遗传力研究

应用数量遗传学的方法分析了水稻二化螟(chilo suppressalis)对杀螟硫磷抗药性的遗传力,并就遗传力和杀虫剂的杀死率对抗性发展速率的影响进行了预测。研究结果表明：二化螟对杀螟硫磷抗性的遗传力较低(h²＝0.277),产生高抗性的潜力不大。即使在室内选择的条件下,要获得10倍的抗性约需要6-12代;在野外条件下则需要更长的时间(15-32代)。因此,结合抗性变化动态的监测结果,我们认为在野外条件下二化螟是不致于产生高抗性,杀螟硫磷仍不失为二化螟抗性治理系统中有效品种之一。     

罗汉果双受精过程的细胞学观察

罗汉果（Ｓｉｒａｉｔｉａｇｒｏｓｖｅｎｏｒｉ（Ｓｗｉｎｇｌｅ）Ｃ．Ｊｅｍｅｙ）双受精过程属有丝分裂前配子融合类型,授粉后２４～４８ｈ,花粉管进入胚囊,穿过一个助细胞,放出两个精子。雌雄核融合和雄核与次生核融合同时发生在授粉后６２～７２,雄核与次生核融合速度快于配子融合,７２ｈ后即可见到初生胚乳核分裂。合子中的雌雄核仁在授粉后第５～６ｄ融合,授粉后８～９ｄ合成分裂形成二细胞胚。在双受精过程中,多次观察到有多条花粉管进入胚囊和多精入极核现象。原胚期有附加花粉管从珠孔进入。     

用于蛋白质同源模建及三维结构预测的结构比较方法

继前面的工作把测试蛋白从三族扩大到十一族,寻求联配参数的普适“缺省值“;比较不同的主链曲率和挠率的计算方法,进一步确认主链的折红红分几何刻划方法的有效性;寻找有效的可变缺失突变惩罚函数的形式。结果表明,编制的蛋白质多重联配软件系统是满意的,可用于蛋白质三维结构预测。     

新型平均势函数在蛋白质反向折叠中的应用

利用蛋白质主链的极性分数及主链二面角为参量,构建了一种基于蛋白质结构数据库的势函数。将该势函数应用于蛋白质反向折叠研究中,发现该函数可成功地将蛋白质分子的天然构象从构建的构象库中识别出来;将一目标序列与构象库的每一可能的构象匹配,并用该势函数计算相应的能量,结果表明对绝大多数蛋白质分子来说,天然的构象的能量值总是最低。此外,该函数还将一些序列相似性较低,而结构相似性较高的蛋白质分子识别出来。我们认     

四川自贡大山铺蜀龙动物群——简报Ⅲ.蜥脚类

本文记述了中侏罗世蜥脚类一新属种——巴山酋龙(Datousaurus bashanensts gen. et sp. nov.)对李氏蜀龙(Shunosaurus lii)的特征进行了补充,讨论了它们在蜥脚类进化过程中的位置。     

Purification of a DNA nicking-closing enzyme from mouse L cells.

A DNA nicking-closing enzyme has been purified from the nuclei of mouse L cells to 90% homogeneity. The denatured and reduced form of the enzyme has a molecular weight of 68,000 which is in agreement with the molecular weight of the native enzyme as determined by gel filtration and by sucrose sedimentation velocity assuming the protein is globular. Therefore, the active form of the enzyme is a monopolypeptide. Its isoelectric point is pH 4.2 +/- 0.2. The nicking-closing activity does not require a cofactor and does not involve any sulfhydryl group. The enzyme requires 0.2 M NaCl and pH in the range of 6.5-7.5 for optimal activity.     

CAMP-dissociation kinetics in hormone-dependent and -independent rat mammary tumor cytosols

Cytosols from 7, 12-dimethylbenz (alpha) anthracene-induced rat mammary tumors which exhibit different hormone-responsiveness were compared with respect to their cAMP-dissociation kinetics. At 22 degree C, pH 4.5, 1 micrometer cAMP, hormone-dependent mammary tumors exhibited monophasic dissociation rates with a rate constant of k-1 = 0.06 min-1. In contrast, hormone-independent mammary tumors exhibited biphasic dissociation curves with rate constants of k-1 = 0.47 and k-2 = 0.06 min-1. The binding of cAMP was completely reversible; radio-labeled ligand was completely dissociated by 1mM nonradioactive cAMP; the binding protein could be reassociated to its original binding level after dextran-coated charcoal adsorption. The mammary cytosols exhibited specific binding for cAMP which could be displaced partially by cGMP but not by ATP, ADP, AMP, or adenosine. Receptor inactivation during the course of incubation was negligible. Both mammary tissue cytosols exhibited similar association rates at 22 degree C, pH 4.5, 1 micrometer cAMP (k+1 = 5-7 x 10(5)M-1 min-1). These data indicate that mammary tissues exhibit 2 cAMP dissociation rates. Hormone-dependent mammary tumors exhibit a dissociation constant of a high affinity binding site (k-1/k+1 = 0.07 micrometer) whereas hormone-independent mammary tumors exhibit dissociation constants of one high affinity (k-1/k+1 = 0.07 micrometer) and a second low affinity site (k-1/k+1 = 0.05 micrometer).