紫云英根瘤菌159中两个结构和功能不同的nodD基因

紫云英根瘤菌１５９含２个拷贝的ｎｏｄＤ基因。核苷酸序列测定表明由ｎｏｄＤ１和ｎｏｄＤ２基因所推定编码的ＮｏｄＤ１和ＮｏｄＤ２蛋白其氨基酸顺序同源性为６９％。功能分析显示,在紫云英根瘤菌中ｎｏｄＤ１和ｎｏｄＤ２基因均能自主表达。由ｎｏｄ１推定的ＮｏｄＤ１能与紫云英种子浸出液（诱导物）共同激活ｎｏｄ基因的表达,而由ｎｏｄＤ２Ｒ推定的Ｎｏｄ２则无此功能。     

氮源对紫云英根瘤菌nod基因表达的作用

高浓度的硫酸铵阻碍了紫云英根瘤菌诱导紫云英根毛发生典型的根毛变形并明显抑制了紫云英结瘤能力。通过对融合子的β-半乳精苷酶活性的测定进一步表明高浓度的硫酸铵对紫云英的结瘤调节基因nodDZ、共同结瘤基因nodA及nodBC的表达有抑制作用而对结瘤调节基因nodD1的表达无抑制作用。     

费氏中华根瘤菌042BS结瘤调节基因的克隆及功能检测

费氏中华根瘤菌 (Sinorhizobiumfredii) 0 4 2BS可以在大豆和苜蓿上结瘤。用费氏中华根瘤菌USDA2 5 7的nodD1和nodD2基因分别作为探针 ,与 0 4 2BS总DNA进行Southern杂交 ,发现其DNA经EcoRI酶切后分别在 3 0kb和 6 0kb处各有一条阳性带。回收这两条阳性带附近的DNA片段 ,建立部分基因文库 ,克隆到带有nodD1基因的 3 0kb片段 ,以及带有nodD2基因的 6 0kb片段。对nodD1和nodD2进行序列分析 ,结果表明 0 4 2BS的nodD1与费氏中华根瘤菌根瘤菌USDA2 5 7和USDA1 91的同源性高达 99% ,而nodD2与USDA2 5 7的同源性为1 0 0 %。再将nodD1的片段克隆到pBBRIMCS 5载体上 ,导入豌豆根瘤菌蚕豆生物变种 (Rhi zobiumleguminosarumbv.viciae)LPR5 0 5 4中进行功能检测 ,显示 0 4 2BS的nodD1均可被大豆分泌的类黄酮物质染料木黄酮以及苜蓿分泌的类黄酮物质毛地黄黄酮所诱导     

苜蓿中华根瘤菌042BM noeAB基因的转录调控

对苜蓿中华根瘤菌(Sinorhizobiummeliloti) 0 4 2BMnoeAB基因的表达调控进行研究。结果发现,葫芦巴碱不能使noeAB的表达水平提高,证明它们的转录不受nodD2的调控。当nodD3和syrM同时存在时,noeAB的表达水平没有明显的变化,表明它们也不受nodD3 syrM系统的调控。在FY基本培养基上,毛地黄黄酮的诱导使noeAB基因的表达水平提高16倍,而在不添加该诱导物的TY培养基上,noeAB基因的表达水平也能够提高30倍以上,说明noeAB是受nodD1控制的,但除受毛地黄黄酮诱导外,noeAB还可能受到其他因子的调节     

苜蓿中华根瘤茵042BM noeAB基因的转录调控

对苜蓿中华根瘤菌(Sinorhizobium meliloti)042BM noeAB基因的表达调控进行研究。结果发现,葫芦巴碱不能使noeAB的表达水平提高,证明它们的转录不受nodD2的调控。当nodD3和syrM同时存在时,noeAB的表达水平没有明显的变化,表明它们也不受nodD3-syrM系统的调控。在FY基本培养基上,毛地黄黄酮的诱导使noeAB基因的表达水平提高16倍,而在不添加该诱导物的TY培养基上,noeAB基因的表达水平也能够提高30倍以上,说明noeAB是受nodD1控制的,但除受毛地黄黄酮诱导外,noeAB还可能受到其他因子的调节。     

苜蓿根瘤菌的正调节蛋白SyrM与nodD3基因P1上游区结合的位点及特性

在苜蓿根瘤菌中 ,nodD3分别由 2个启动子P1和P2在不同条件下介导表达 .通过凝胶滞后技术进一步研究与nodD3基因P1介导表达有关的反式作用因子 ,证明SyrM能与P1上游区结合 ,而NodD3则不能 ,因而排除了NodD3直接自身激活的可能性 .利用DNA酶Ⅰ足印分析确定了SyrM结合于nodD3基因P1上游区的顺式因子序列 ,在该序列中含有 2个顺向重复的反转重复结构 .通过合成的只含有 1个反转重复结构的 3种寡核苷酸片段与SyrM进行结合分析 ,结果表明SyrM不能与它们结合 ,因此SyrM可能是以二聚体或四聚体的形式与该顺式因子结合     

紫云英根瘤菌基因组中存在有类似IS因子的DNA重复顺序

在紫云英根瘤菌(Rhizobium astragali)的基因组中存在有DNA重复顺序(RSRa)。它在Ra159的基因组中重复4～5次,其中一个拷贝位于nifH基因的上游。以1.25kbPvul片段作探针,在其他紫云英根瘤菌菌株及豌豆根瘤菌RI PRE中也都检测到与RSRa同源的DNA片段。序列测定的结果表明RSRa其结构类似于IS因子,具有原核插入顺序的一些特点。RSRa全长1468bp,在RSRa的两个末端具有反向重复顺序,RSRa中有一个大的开放阅读框架(ORF)。由ORF推定的蛋白与大肠杆菌插入顺序IS903推定的转座酶有较高的同源性。     

苜蓿根瘤菌(Sinorhizobium meliloti)nodD3P1启动子下游序列的缺失和互补分析

在苜蓿根瘤菌中,nodD3基因的转录由两个彼此分离的启动子P1和P2控制. 在P1下游是一段由660 bp组成的序列, 接着是nodD3的编码区. 由P1下游序列3′末端开始缺失得到的一系列缺失突变体的遗传分析指出, P1下游＋1~＋125 nt序列对P1的表达是必须的. 互补分析和结瘤试验指出, ORF2自我抑制P1的表达, 而＋1~＋125 nt序列可对抗ORF2对P1的抑制作用.     

苜蓿中华根瘤菌042BMnoeAB基因的转录调控

对苜蓿中华根瘤菌（Sinorhizobium meliloti）042BM noeAB基因的表达调控进行研究。结果发现,葫芦巴碱不能使noeAB的表达水平提高,证明它们的转录不受nodD2的调控。当nodD3和syrM同时存在时,noeAB的表达水平没有明显的变化,表明它们也不受nodD3syrM系统的调控。在FY基本培养基上,毛地黄黄酮的诱导使noeAB基因的表达水平提高16倍,而在不添加该诱导物的TY培养基上,noeAB基因的表达水平也能够提高30倍以上,说明noeAB是受nodD1控制的,但除受毛地黄黄酮诱导外,noeAB还可能受到其他因子的调节。     

豌豆根瘤菌结瘤基因启动子内二级结构区与转录活性有关

用羟胺随机改变豌豆根瘤菌(Rhizobium leguminosarum)结瘤基因 nodD上游的调控区间的核苷酸顺序,将它们插入广谱转录质粒pMP220的LacZ基因前,启动LacZ基因的表达、突变表明与结瘤基因的转录活力有关.DNA序列分析发现,这些突变都在距nodD基因起始密码子约80bp的二级结构区内.     

Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

It has now been over twenty years since a novel herpesviral genome was identified in Kaposi's sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi's sarcoma-associated herpesvirus(KSHV; also known as human herpesvirus 8(HHV-8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.     

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     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.