RecA, Tus protein and constitutive stable DNA replication inEscherichia coli rnhA mutants

Constitutive stable DNA replication (cSDR), which uniquely occurs inEscherichia coli rnhA mutants deficient in ribonuclease HI activity, requires RecA function. TherecA428 mutation, which inactivates the recombinase activity but imparts a constitutive coprotease activity, blocks cSDR inrnhA mutants. The result indicates that the recombinase activity of RecA, which promotes homologous pairing and strand exchange, is essential for cSDR. Despite the requirement for RecA recombinase activity, mutations inrecB, recD, recJ, ruvA andruvC neither inhibit nor stimulate cSDR. It was proposed that the property of RecA essential for homologous pairing and strand exchange is uniquely required for initiation of cSDR inrnhA mutants without involving the homologous recombination process. The possibility that RecA protein is necessary to counteract the action of Tus protein, a contra-helicase which stalls replication forks in theter region of the chromosome, was ruled out because introduction of thetus : :kan mutation, which inactivates Tus protein, did not alleviate the RecA requirement for cSDR.     

Isolation and Characterization of the Plasma Membrane by Two-Phase Partitioning from the Alkalophilic Cyanobacterium Spirulina platensis

Partition in aqueous dextran-polyethylene glycol two-phase systemwas used to isolate the plasma membranes from the alkalophiliccyanobacterium Spirulina platensis. The upper phase containeda colorless membranes obtained in relatively short time, 3–4h. This fraction had a different protein profile than that ofthe thylakoid fraction obtained in the lower phase. It did notcontain cytochrome c-oxidase activity, but retained characteristicMg²⁺-ATPase activity that is sensitive to vanadate, stimulatedby K⁺, and has a pH optimum near 8.5. These data support ourassumption that the upper phase of the gradient consist of theplasma membrane of S. platensis. (Received November 25, 1993; Accepted April 12, 1994)     

Transfection of the mouse ICAM-1 gene into murine neuroblastoma enhances susceptibility to lysis,reduces in vivo tumorigenicity and decreases ICAM-2-dependent killing

We determined the expression of intercellular adhesion molecules (ICAM) on neuro-2a cells in order to evaluate whether they were involved in cytolysis of murine neuroblastoma. Fluorescence-activated cell sorting analysis revealed that the control neomycin-resistance-genetransduced line (neuro-2a/LN) had poor expression of ICAM-1 (mean channel fluorescence, MCF=3.7). An ICAM-1-positive transfectant of neuro-2a (neuro-2a/ICAM-1⁺) (CMF=64.3) was generated to evaluate directly the role of this adhesion molecule in cytolysis. Neuro-2a/ICAM-1⁺ was more sensitive to LAK killing (69.7% at an effector-to-target ratio of 1001) compared to neuro-2a/LN (48.6%) (P<0.001). Blocking of neuro-2a/LN and neuro-2a/ICAM-1⁺ lysis with anti-ICAM-1 monoclonal antibodies (mAbs) did not account for all the LFA-1-dependent killing. These data indicate that even in neuro-2a/ICAM-1⁺ cells, other LFA-1 ligands participated in the effector-target interaction. Therefore, we examined these cell lines for ICAM-2 expression. Both neuro-2a/LN and neuro-2a/ICAM-1⁺ lines expressed ICAM-2 (MCF=16.4 and 16.5). ICAM-2 accounted for the majority of the LFA-1-dependent killing in the ICAM-1-negative target, neuro-2a/LN, while ICAM-1 played a primary role in the cytolysis of the ICAM-1⁺ transfectant. Inhibition of lysis in the presence of anti-ICAM-1 and ICAM-2 mAbs was comparable to that seen with the addition of anti-LFA-1 mAb, indicating that other LFA-1 ligands were not involved in this system. ICAM-1 expression was associated with decreased in vivo tumorigenicity; mice inoculated with neuro-2a/ICAM-1⁺ cells had a significantly longer survival compared to those receiving neuro-2a/LN cells (median survival time 35.5 versus 24.5 days) (P<0.001). It is important to note that ICAM-1 transfection of murine neuroblastoma did not alter its metastatic potential. We conclude that transfection of mouse neuroblastome with ICAM-1 increases its sensitivity to in vitro lysis and reduces its in vivo tumorgenicity. In ICAM-1-negative murine neuroblastoma cells, ICAM-2 plays a primary role in cell-mediated lysis.This work was supported in part by the Children's Cancer Research Fund, the Minnesota Medical Foundation, the Viking Children's Fund and NIH grants PO1-CA-21737, NO1-AI-85002. E. K. is a recipient of the Irvine McQuarrie Research Scholar Award and B. R. B. a recipient of the Edward Mallinkrodt Foundation Scholar Award     

滇蜀豹子花核型及其变异研究

本文详细报道了滇蜀豹子花的核型,发现居群中存在两种细胞型,即A型和B型。A型参考核型为2n = 24＝2m(2SAT)+2sm+8st(4SAT)+12t(2SAT),其第3号两条同源染色体长臂均无居间随体：B型参考核型为2n=24＝2m(2SAT)+2sm+8st(2SAT)+12t(3SAT)+0—1b,其第3号一条同源染色体长臂紧靠着丝点处有一大而明显的居间随体,而另一条同源染色体则无,构成明显的3号染色体的结构杂合性。统计表明,居群中二者的比例近似为1A;2B。研究还发现了大量的体细胞染色体结构变异核型,表明滇蜀豹子花核型尚未趋于稳定,还处于强烈分化之中,高频率的体细胞染色体结构变异是其种内分化不可忽视的一种进化要素。     

孔药花属(鸭跖草科)的核型研究

本文首次对鸭跖草科孔药花属Porandra Hong进行染色体研究。孔药花P．ramosa Hong和攀缘孔药花P．scandens Hong在染色体的大小、数目和形态上都十分相似,核型公式为2n＝36＝4m+26sm+6st(2sat),核型类型属于3B。染色体证据支持孔药花属与穿鞘花属Amischotolype和Coleotrype属相近的观点。     

菜用香椿良种选育性状的模糊综合评判

采用模糊数学方法对菜用香棒１６个不同种源的无性系从形态、颜色、香气、抗病性四个方面进行了综合评判,筛选出了接近选育目标的５个菜用优良无性系。     

油松鳞叶中细胞核穿壁现象的初步研究

利用薄切片和超薄切片技术对油松衰老鳞叶中细胞核穿壁运动进行了观察研究。首次,细胞核内的染色质逐渐收缩集中,形成染色深的球状体,以后,细胞核逐渐与细胞壁接近。接着紧贴细胞壁的细胞核通过细胞壁上的通道或胞间连丝转移到相邻的细胞内,此外,还发现有多种其它的转移方式存在。研究结果表明细胞核的穿壁运动现象同时存在于连子植物和裸植物中,电镜观察进一步证明细胞壁道在细胞核穿壁之前已形成。     

蜜蜂脑中5—HT，GABA，Ach免疫反应阳性神经元分布的比较研究

通过免疫细胞化学方法－ＰＡＰ法,研究了中华峰（Ａｐｉｓｓｉｎｅｎｓｉｓ）和意大利峰（ＡｐｉｓｍｅｌｌｉｆｅｒａＬ）脑和视叶中乙酰胆碱（Ａｃｈ）、５－羟色胺（５－ＨＴ）、γ－氨基丁酸（ＧＡＢＡ）免疫反应阳性神经元胞体和纤维的形态、染色强度、分布和各种神经丛之间的联系．一方面将这些阳性分布系统和蜜蜂脑中相应的神经元类型进行比较,另一方面也分析了在一些特殊解剖学通路中存在的可能的神经递质及其作用．     

Complex duplications in maize lines

Rp1 is a disease resistance complex and is the terminal morphological marker on the short arm of maize chromosome 10. Several restriction fragment length polymorphisms (RFLPs), which map within 5 map units of Rp1, were examined to determine if they are also complex in structure. Two RFLP loci, which mapped distally to Rp1, BNL3.04 and PIO200075, existed in a single copy in all maize lines examined. These two loci cosegregated perfectly in 130 test cross progeny. Two RFLP loci that map proximally to Rp1 had unusual structures, which have not yet been reported for maize RFLPs; the loci were complex, with variable numbers of copies in different maize lines. One of the loci, NPI285, occasionally recombined in meiosis to yield changes in the number of copies of sequences homologous to the probe. The other proximal locus, detected by the probes NPI422, KSU3, and KSU4, was relatively stable in meiosis and no changes in the number of restriction fragments were observed. The similarity in map position between Rp1 and the complex RFLP loci indicate there may be genomic areas where variable numbers of repeated sequences are common. The structure of these complex loci may provide insight into the structure and evolution of Rp1.