An 18-base-pair sequence is sufficient for termination of rolling-circle replication of plasmid pT181.

pT181 and related plasmids of gram-positive bacteria replicate by a rolling-circle mechanism. The replication initiator protein of pT181, RepC, has origin-specific nicking-closing activities. Replication of the plasmid pT181 leading strand initiates by covalent extension of the RepC-generated nick, and the origin of replication contains signals for both initiation and termination of DNA replication. We have investigated the sequence requirements for the initiation and termination steps by using plasmids containing two pT181 origins. In vitro replication experiments showed that 18- and 24-bp synthetic oligonucleotides containing the RepC nick site were active in the termination of replication. However, initiation of replication required a larger region which also includes the RepC binding site. Plasmids containing the 18- and 24-bp region were also found to be nicked by the RepC protein. Our results demonstrate that sequence requirements for initiation and termination of pT181 replication overlap, but while the RepC binding site is required for initiation, it is dispensable for termination.     

神经敏感性的降低是棉铃虫对拟除虫菊酯抗药性的重要机制

用扫描电子显微镜和光学显微镜的染色观察,研究了棉铃虫Helicoverpa armigeraHubner 3龄幼虫腹部神经一肌肉的分布,表明其腹纵肌细胞适合于作电生理细胞内记录。用电生理细胞内微电极记录法研究了棉铃虫三个品系：对照品系、功夫菊酯抗性品系(Cy-R,抗性指数13.4)和氰戊菊酯抗性品系(Fn-R,抗性指数37.9)的3龄幼虫神经一肌肉材料对相应杀虫剂的神经敏感性。结果表明：用10^-6mol/L的功夫菊酯处理Cy-R,在30min内有40%的个体对药剂无反应,另外60%的个体产生反应所需的时间是对照品系的3.5倍。用10^-6mol/L的氰戊菊酯处理Fn-R,在30min内有47%的个体对药剂无反应,另外53%的个体产生反应所需的时间是对照品系的4.2倍。这些结果说明神经敏感性降低是棉铃虫对拟除虫菊酯抗药性的重要机制。     

内源植物激素与光敏核不育水稻农垦58S育性的关系

采用气相色谱－质谱联用选择离子检测（ＧＣ－ＭＳ－ＳＩＭ）技术,定性、定量分析了光敏核不育水稻农垦５８Ｓ（Ｏｒｙｚａ ｓａｔｉｖａ Ｌ． ｓｕｂｓｐ． ｊａｐｏｎｉｃａ）及对照品种“农垦５８”在长（ＬＤ）、短（ＳＤ）日照处理下,不同发育时期顶端全展叶片中内源ＩＡＡ、ＡＢＡ 和生殖器官中内源ＩＡＡ、ＡＢＡ、ＧＡ１、ＧＡ４ 的含量变化。实验结果表明：在ＬＤ 处理下,农垦５８Ｓ雌雄蕊形成期的叶片和花粉母细胞形成期的幼穗中ＩＡＡ 相继发生亏缺;农垦５８Ｓ－ＬＤ花粉母细胞形成期、单核期和扬花期,生殖器官中内源ＡＢＡ 均低于农垦５８Ｓ－ＳＤ 的含量,“农垦５８”则与此相反;扬花期不育花药中内源ＧＡ１ 和ＧＡ４ 含量剧减。据此认为：生殖器官中早期ＩＡＡ 的亏损、ＡＢＡ 含量剧减伴随着抗逆性能的减弱及ＧＡＳ的不足共同导致了农垦５８Ｓ的雄性败育     

蓝藻藻胆体与类囊体膜之间光能传递的研究

从嗜热蓝藻优雅粘囊藻（Ｍｙｘｏｓａｒｃｉｎａ ｃｏｎｃｉｎｎａ Ｐｒｉｎｔｚ．）中分离到具有放氧活性的藻胆体－类囊体膜复合物。它的吸收峰位于６８０、６２８、４９０、４３８和４２０ ｎｍ ,在低离子强度（０．１～０．４ ｍ ｏｌ／Ｌ）磷酸缓冲液中的６６４ ｎｍ 荧光发射峰随离子强度的降低而升高,７１８ ｎｍ 荧光发射峰与此相反（７７ 。Ｋ,Ｅｘ＝ ５８０ ｎｍ ）。当把游离的藻胆体和已解离去藻胆体的类囊体膜在蔗糖磷酸缓冲液中重组时,随时间延长（０～６０ ｍ ｉｎ）,７１８ ｎｍ 荧光发射峰逐渐升高,６８５ ｎｍ 荧光发射峰逐渐下降（７７ 。Ｋ,Ｅｘ ＝ ５８０ ｎｍ ）,表明藻胆体与类囊体之间的解离和结合对光能传递的影响     

九种罕见的人类染色体异常核型报告

ReportonNineRareSpeciesofHumanChromosomalAbnormalKaryotypesHanWeitian;QuOu;YuPing;JiangMiao(LiaoningResearchInstituteofFamilyPlanning,Shenyang110031)自1983年以来,我们对数千例不育及胚胎丢失等生殖异常患者进行细胞遗传学研究,发现大量异常染色体核型,而且异常种类繁多,已报道世界首报人类异常核型25种[1]。最近,在不良妊娠患者中又发现9种异常核型,经湖南医科大学医学细胞遗传学国家培训中心鉴定,为世界首次报道．现报告如下。1病例摘要及核型例1男,30岁,表型及智力正常,其妻子妊娠两次,均在无任何诱因情…     

大肠癌中p53基因突变的研究

应用聚合酶链反应(PCR)──单链构型多态性(SSCP)结合银染法对14例大肠癌p53基因的第4、第5─6和第7外显子进行了点突变的研究,结果共检测出6例点突变,而且发现各外显子的突变频率存在差异。另外,利用购自ATCC的两个探针 (p53cDNA探针和pYNZ22探针)对大肠癌中p53基因的杂合性失去进行了研究,在14例大肠癌中共检出6例杂合性丢失。将点突变检测结果同杂合性丢失结果进行比较分析, 并着重探讨了大肠癌中p53基因失活导致肿瘤的作用方式。 Abstract:The exons 4-7 of p53 gene were examined in 14 colorectal Cancer patients by using PCR-SSCP-silver staining method.The results showed 6 cases of point mutation and the mutation frequencies of exons were different from each other.p53 cDNA and pYNZ22 VNTR were used as probes to examine LOH(Loss of heterozygosity)of 14 colorectal cancers.6 cases with LOH were found.The results of present research suggest that mutation and LOH of p53 gene are critical events in the progress and development of Cancer.There were different kinds of inactivation model of p53 gene in the process of development of cancer and transformation of cells.     

Effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic acetylcholine receptors on transmembrane potentials and currents in guinea pig ventricular myocytes

The effects of anti-peptide antibodies against the second extracellular loop of human M2 muscarinic receptor on transmembrane potentials and currents in guinea pig single ventricular cells were analyzed using whole-cell patch clamp technique. These effects were compared with those of the muscarinic receptor agonists carbachol and acetylcholine. The antibodies shortened the action potential duration in a dose-dependent manner. By using a ramp or step rectangular pulse protocol, it was found that the antibodies increased the outward K⁺ current and decreased the inward basal I Ca significantly. The reversal potential of both carbachol-and antibody-induced extra currents were close to –80 mV, being in proximity to the calculated E_k of –90 mV. A -adrenergic receptor agonist, isoprenaline, prolonged the action potential and increased the overshoot which could be inhibited by both antibody and carbachol. Isoprenaline increased inward I_ca and outward I_k simultaneously. Both antibody and carbachol could significantly reduce the isoprenaline-stimulated I_Ca but not the isoprenaline-stimulated I_k. The antibody- or carbachol-induced outward K⁺ current and the depressant effects of antibody and carbachol on isoprenaline-stimulated I_ca were partially antagonized by atropine. These results suggest that the anti-M2 muscarinic receptor antibodies display a stimulatory activity similar to muscarinic receptor agonist on the receptor-mediated electrophysiological events.     

The structure of d(TpA), the major photoproduct of thymidylyl-(3'5')-deoxyadenosine.

Irradiation of the dinucleotide TpdA and TA-containing oligonucleotides and DNA produces the TA* photoproduct which was proposed to be the [2+2] cyclo-addition adduct between the C5-C6 double bonds of the T and the A [Bose,S.N., Kumar,S., Davies,R.J.H., Sethi,S.K. and McCloskey,J.A. (1984) Nucleic Acids Res. 12, 7929-7947]. The proposed structure was based on a variety of spectroscopic and chemical degradation studies, and the assignment of a trans-syn-I stereochemistry was based on an extensive 1H-NMR and molecular modeling study of the dinucleotide adduct [Koning,T.M.G., Davies,R.J.H. and Kaptein,R. (1990) Nucleic Acids Res. 18, 277-284]. However, a number of properties of TA* are not in accord with the originally proposed structure, and prompted a re-evaluation of the structure. To assign the 13C spectrum and establish the bond connectivities of the TA* photoproduct of TpdA [d(TpA)*], 1H-13C heteronuclear multiple-quantum coherence (HMQC) and heteronuclear multiple bond correlation (HMBC) spectra were obtained. The 13C shifts and connectivities were found to be inconsistent with the originally proposed cyclobutane ring fusion between the thymine and adenine, but could be explained by a subsequent ring-expansion reaction to give an eight-membered ring valence isomer. The new structure for the d(TpA)* resolves the inconsistencies with the originally proposed structure, and could have a stereochemistry that arises from the anti, anti glycosyl conformation found in B form DNA.