大肠杆菌棉子糖操纵子

大肠杆菌（Ｅscherichia coli）棉子糖（raf）操纵子位于质粒,它编码能够使大肠杆菌吸收和利用三糖棉子糖的蛋白,即一个主动运输系统（Ｒaf透性酶）,α－关乳糖苷酶和蔗糖水解酶。raf操纵子包括启动子rafP,调节基因rafR,操纵基因rafO以及rafA,rafB,rafD三个结构基因。这个操纵子一个阻遏蛋白RafR负控制,同时以环腺苷－代谢降解物基因激活蛋白（cAMP-CAP）为中介的正调控也参与调节。     

大肠杆菌棉子糖操纵子a-半乳糖苷酶表达的调节控制

大肠杆菌棉子糖操纵子(raf)位于质粒,其第一结构基因rafA编码的a-半乳糖苷酶为诱导酶。Rat操纵子比乳糖操纵子(lac)或蜜二糖操纵子(mel)对诱导物有更严格的结构特异性。该酶被蜜二糖或棉子糖诱导,也被D-半乳糖微弱诱导,但不受乳糖、PNPG等结构相近糖所诱导。A-半乳糖苷酶的酶诱导形成能力在对数生长末期出现高峰。Rat 操纵子基因结构组成及调节与乳糖操纵子相似。以阻遏物为中介的负调控在raf操纵子调节中起主要作用,同时以环腺苷一代谢降解物基因激活蛋白(cAMP-CAP)为中介的正调控也参与调节。当0．4％葡萄糖加入到其它碳源培养基时,该酶表达水平下降至原活力的1／2—1／3。无论诱导或组成型酶的葡萄糖抑制均未见瞬时抑制。腺苷环化酶(cya)缺失或环腺苷受体蛋白(crP)和cya双缺陷菌株的酶表达则分别下降到原活力的9％和2．5％。Cya突变株或葡萄糖对raf操纵子表达的抑制可被cAMP解除,但cya和crP双缺陷菌株仍有葡萄糖抑制,而且这种抑制不为cAMP抵消,表明通过降低cAMp而影响cAMP-CAP复合体形成还不能解释代谢降解物抑制的全部机制。尚无证据说明吲哚类小分子化合物和低浓度尿素对raf操纵子表达的明显作用。     

大肠杆菌α—D—半乳糖苷酶的提纯及特性

大肠杆菌中与抗原K(?)s ab基因相连锁的棉子糖操纵子(raf)编码的α-D-半乳糖苷酶经硫酸铵沉淀,Sepharose 4B和DEAE纤维素等提纯步骤获纯化品,其在PAGE上呈单一电泳区带,分子量80000。粗酶品经Sepharose 4B后呈现为两个酶活性峰。该酶特性与染色体编码的同功酶有明显差异。最适温度为35—37℃,最适pH 7.5。以PNPG、蜜二糖、棉子糖为底物,其米氏常数分别为0.11,2.1和136mmol/L。Mn~2 离子影响酶稳定性,然而可以被巯基试剂消除。双扩散免疫实验初步表明,产H_2S基因连锁的raf操纵子编码的α-D-半乳糖苷酶与该酶可能具有相同抗原性。     

大肠杆菌α-D-半乳糖苷酶的提纯及特性*

大肠杆菌中与抗原K(?)s ab基因相连锁的棉子糖操纵子(raf)编码的α-D-半乳糖苷酶经硫酸铵沉淀,Sepharose 4B和DEAE纤维素等提纯步骤获纯化品,其在PAGE上呈单一电泳区带,分子量80000。粗酶品经Sepharose 4B后呈现为两个酶活性峰。该酶特性与染色体编码的同功酶有明显差异。最适温度为35—37℃,最适Ph 7.5。以PNPG、蜜二糖、棉子糖为底物,其米氏常数分别为0.11,2.1和136mmol/L。Mn²⁺离子影响酶稳定性,然而可以被巯基试剂消除。双     

大肠杆菌鼠李糖调节子

大肠杆菌（Escherichia coil）L-鼠李糖（rha）调节子由三个功能相关的操纵子（operon）组成,位于大肠杆菌染色体基因组中。它编码大肠杆菌吸收和利用L-鼠李糖的蛋白,即一个鼠李糖运输蛋白（RhaT）、三个鼠李糖代谢酶（RhaB、RhaA、RhaD）以及两个调节蛋白（RhaS、RhaR）。三个操纵子均受到L-鼠李糖本身的诱导,同时以调控蛋白RhaS、RhaR和CRP（cAMP受体蛋白）为中介的正调控也参与调节。     

青霉素酰化酶操纵子为负调控模型

质粒pBR322用HindⅢ—BarnH Ⅰ双酶切作为载体,从质粒pPAd上克隆含有pac操纵基因的HindⅢ一。BglⅡl．65kb的DNA片段,得到质粒pPA41。质粒pBR322和pPA41转化染色体上含有完整pac操纵子的大肠杆菌D816,进行操纵基因滴定。大肠杆菌D816、D816(pPA4l)．D816(pBR322)在22℃摇瓶发酵96h,NIPAB法测定青霉素酰化酶活性。结果发现,在不加诱导剂时,D816(pPA41)产生的青霉素酰化酶是D816细胞的2．5倍,在加诱导剂时,D816(pPA41)产生的青霉素酰化酶是D816细胞的1．3倍。对照组D816(pBR322)细胞产生的青霉素酰化酶和：D816细胞产生的几乎一致,说明质粒pPA41的竞争滴定作用确是其上克隆的操纵基因引起的。高拷贝的操纵基因(pPA41)和pac操纵子竞争结合调节蛋白,使得pac操纵子表达增加,说明调节蛋白在pac操纵子表达过程中起阻遏作用,调节蛋白为阻遏蛋白,pac操纵子为负调控模型。R．NA—DNA点杂交检测pac基因表达,发现D816(pPA41)细胞转录产生的pac—mRNA量明显高于D816细胞,mRNA量和青霉素酰化酶活性呈现一致的趋势,证实了pac操纵子的负调控发生在转录水平。     

乙型肝炎病毒表面抗原基因在大肠杆菌中的表达

通过次级克隆我们组建了乳糖操纵子启动基因控制下的乙型肝炎病毒表面抗原(HBsAg)基因片段和乙型肝炎病毒(HBV)基因组两种表达质粒,能在大肠杆菌中合成β-半乳糖苷酶乙型肝炎病毒表面抗原杂合蛋白,可被放射免疫分析和蛋白凝胶电泳所检测。     

激素和活性多肽

一个预先制备的与thymulin有关的合成基因被连接到被酶切的质粒pJB1301上,并用之转化大肠杆菌(Escherichia)CAGll39。该基因被置于 Lac操纵子     

第10届国际生物奥林匹克竞赛(1999)理论试题(三)

(续 2 0 0 0年第 35卷第 7期第 4 4页 )理论试题 B部分 :B部分的所有题目为多项选择题 ,但答案数目不一定 ,可能有一个、几个或全部为正确答案。答题时你必须准确地选出正确答案 ,并在正确选项前的横线上标 。细胞生物学、微生物学和生物工程学4 6　大肠杆菌的乳糖操纵子基因是典型的 (最优秀的 ) ;从此创造了操纵子概念 ,提出操纵子概念的研究者获得了诺贝尔奖金。大肠杆菌乳糖操纵子含有 3个基因 :z.编码 β-半乳糖苷酶 ,y.编码 β-半乳糖透过酶 ,a.编码转乙酰酶。变构乳糖是乳糖的异构体 ,这是通过 β-半乳糖苷酶产生的中间体 ,半乳糖…     

A Unique Protease Cleavage Site Predicted in the Spike Protein of the Novel Pneumonia Coronavirus (2019-nCoV) Potentially Related to Viral Transmissibility

正Dear Editor,In December 2019, a novel human coronavirus caused an epidemic of severe pneumonia(Coronavirus Disease 2019,COVID-19) in Wuhan, Hubei, China(Wu et al. 2020; Zhu et al. 2020). So far, this virus has spread to all areas of China and even to other countries. The epidemic has caused 67,102 confirmed infections with 1526 fatal cases     

Curcuminoids as inhibitors of thioredoxin reductase: A receptor based pharmacophore study with distance mapping of the active site

Curcumin is the yellow pigment of turmeric that interacts irreversibly forming an adduct with thioredoxin reductase (TrxR), an enzyme responsible for redox control of cell and defence against oxidative stress. Docking at both the active sites of TrxR was performed to compare the potency of three naturally occurring curcuminoids, namely curcumin, demethoxy curcumin and bis-demethoxy curcumin. Results show that active sites of TrxR occur at the junction of E and F chains. Volume and area of both cavities is predicted. It has been concluded by distance mapping of the most active conformations that Se atom of catalytic residue SeCYS498, is at a distance of 3.56 from C13 of demethoxy curcumin at the E chain active site, whereas C13 carbon atom forms adduct with Se atom of SeCys 498. We report that at least one methoxy group in curcuminoids is necessary for interation with catalytic residues of thioredoxin. Pharmacophore of both active sites of the TrxR receptor for curcumin and demethoxy curcumin molecules has been drawn and proposed for design and synthesis of most probable potent antiproliferative synthetic drugs.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

New or rare chromosome counts in Artemisia L. (Asteraceae, Anthemideae) and related genera from Kazakhstan

Fifteen chromosome counts of six Artemisia taxa and one species of each of the genera Brachanthemum, Hippolytia, Kaschgaria, Lepidolopsis and Turaniphytum are reported from Kazakhstan. Three of them are new reports, two are not consistent with previous counts and the remainder are confirmations of very scarce (one to four) earlier records. All the populations studied have the same basic chromosome number, x = 9, with ploidy levels ranging from 2x to 6x. Some correlations between ploidy level, morphological characters and distribution are noted.     

肝癌中HBV和HCV基因和抗原的分布及意义

采用原位分子杂交方法检测HCV RNA及HBV X基因;采用免疫组织化学方法研究HCV核心抗原,非结构区C33c抗原及HBxAg在肝细胞肝癌中的定位及分布.结果表明(1)HCV RNA、HBV X基因在肝细胞肝癌组织检出率分别为40%(55/136)和82%(112/136).HCV RNA定位于癌细胞的胞浆内,阳性细胞呈散在、灶状及弥漫分布三种形式;HBV X基因在肝癌细胞中的分布呈胞浆型、核型及核浆型,阳性细胞也呈上述三种分布形式;(2)HCV C33c抗原、核心抗原在肝细胞肝癌中的阳性率为81%(133/164)及86%(141/164).C33c抗原定位于癌细胞及肝细胞的胞浆内;核心抗原既定位于癌细胞核中,又可定位于胞浆中.C33c抗原阳性细胞以灶状分布为主;而核心抗原阳性细     

Comparative morphology of the carpel in the Liliaceae: Hewardieae, Petrosavieae, and Tricyrteae

The young pistils in the melanthioid tribes, Hewardieae, Petrosavieae and Tricyrteae, are uniformly tricarpellate and syncarpous. They lack raphide idioblasts. All are multiovulate, with bitegmic ovules. The Petrosavieae are marked by the presence of septal glands and incomplete syncarpy. Tepals and stamens adhere to the ovary in the Hewardieae and the Petrosavieae but not in the Tricyrteae. Two vascular bundles occur in the stamens of the Hewartlieae and Tricyrtis latifolia. Ventral bundles in the upper part of the ovary of the Hewardieae are continuous with compound septal bundles and placental bundles in the lower part. Putative ventral bundles occur in the alternate position in the Tricyrteae and putative placental bundles in the opposite. position in the Petrosavieae. The dichtomously branched stigma in each carpel of the Tricyrteae is supplied by a bifurcated dorsal bundle.