The origin of the DNA in a special class of generalized transducing particles of Salmonella-phage P22

Summary A special class of transducing particles in lysates of P22 is described. When DNA synthesized after infection is density labelled with bromodeoxyuridine, this class of particles exhibit a higher density in CsCl-gradients than normal transducing particles in the same lysates. It is shown that the DNA of these transducing particles carries the normal amount of bacterial information and is synthesized in the semiconservative mode after phage-infection. From the efficiency of BU-incorporation we conclude that the DNA molecules of these particles are not products of normal bacterial replication, but might be replicated under the control of the phage.     

Functional classification of P22 Amber mutants

Summary Eleven cistrons of genes active in lytic growth of phage P22 were classified by phenotypic expression of their amber mutants in nonpermissive Salmonella typhimurium. Seven cistrons code for late functions according to their lysis positive phenotype. Of the remaining four cistrons one codes for lysozym synthesis, two for phage directed DNA synthesis and one seems to be engaged in regulation of late gene expression.The majority of the experiments presented are a part of the dissertation of H. D. Dopatka submitted 1971 to the University of Göttingen.     

Amber-Mutanten des Salmonella-Bakteriophagen P22

Ohne Zusammenfassung     

Salmonella typhimurium mutants affecting establishment of lysogeny

Summary Salmonella typhimurium mutants have been isolated in which phage P22 fails to establish lysogeny. These appear to be defective in cAMP metabolism. A phage mutation overcoming the bacterial defect has been mapped between gene c ₁ and gene 12.     

Ant-mediated transactivation of early genes in Salmonella prophage P22 by superinfecting virulent P22 mutants

Summary The virulent mutants P22 vir B vy and P22 vy mutants, both insensitive to mnt-repressor, transactivate the early genes of a P22 prophage. The transactivation of early P22 prophage genes depends strictly on the expression of gene ant (antirepressor-protein) by the superinfecting P22 mutant and therefore occurs by derepression.     

Altered cotransduction frequencies exhibited by HT-mutants of Salmonella-phage P22

Summary A procedure is described that permits the selection of functionally deficient, temperature sensitive mutants of tobacco mosaic virus based upon the time of local lesion formation on the appropriate host plant.     

Integration defective mutants of bacteriophage P2

Summary Mutants of phage P2 unable by themselves to be integrated as prophages have been isolated. These mutants (int) are complemented by the wild type allele and may then yield stable lysogenic strains carrying an int prophage at location I in Escherichia coli C. These lysogens produce either no phage or little phage, depending on the int mutant used. All int mutants isolated appear to belong to a single complementation group.Exceptional lysogens carrying two or more int prophages may be obtained: they may produce spontaneously even more phage than normal lysogens, and they segregate out defective, singly lysogenic clones at low frequency. These exceptional lysogens carry both prophages in location I, presumably in tandem.Strains carrying two or more int prophages but defective in phage production were also isolated. One of these carries its prophages at two different, not closely linked, chromosomal locations.     

Cis-trans position effect in Salmonella phage P22

Summary Two nonsense mutants of Salmonella form a burst size in mixed infection of non-permissive bacteria which lies above that for non-complementing pairs but below that expected for complementation. The two mutants map closely together.To determine whether the two mutants reside in different genes or in the same gene, single bursts following mixed infection of non-permissive bacteria were analyzed for the relative frequency of wild type versus mutant phage. The results indicate that the two mutants lie in two neighboring genes. The mutants exhibit a cis-trans position effect characteristic of structural genes in bacterial operons.     

Characterization of Pseudomonas aeruginosa mutants deficient in the establishment of lysogeny.

Mutants of Pseudomonas aeruginosa with impaired ability to establish a lysogenic relationship with temperate bacteriophage (Les-) have been isolated. These les mutations map to two areas of the P. aeruginosa chromosomal map as determined by conjugational and transductional analyses. Two phenotypic classes of Les- mutants were identified. One class of mutations has pleiotropic effects on DNA metabolism. These mutants are unable to recombine genetic material acquired as a result of either conjugation or transduction (Rec-). In addition, the ability of these Les- Rec- mutants to repair UV-induced damage to bacteriophage is reduced (host-cell reactivation deficient, Hcr-). Mutants of the second class are Les-, Rec+, and Hcr+.     

核糖体bS22、bL37基因的敲除增强分枝杆菌对抗生素的敏感性

近年来,利用冷冻电子显微镜在分枝杆菌(mycobacteria)的核糖体中新发现了两个蛋白：位于30S亚基解码中心附近的bS22和位于50S亚基肽酰转移酶中心附近的bL37。由于这两个蛋白均邻近抗生素与核糖体结合区,推测它们可能会影响相关药物与靶点的结合。因此我们利用同源重组的方法,在野生型耻垢分枝杆菌(Mycolicibacterium smegmatis) mc2155中分别敲除这两个蛋白的编码基因,并测定菌株的生长曲线和对相关抗生素的敏感性。结果表明,与野生型相比,2株敲除株的生长速率均没有显著变化,但菌株ΔbS22相比于野生型对卷曲霉素、卡那霉素、阿米卡星、链霉素、庆大霉素、巴龙霉素和潮霉素B的敏感性增加,菌株ΔbL37相比于野生型对利奈唑胺的敏感性增加,并且这种敏感性的变化通过基因回补均得到恢复。研究结果暗示了核糖体蛋白bS22、bL37作为药物设计靶点的可能性。     

Taxonomic differences among closely related pines Pinus sylvestris, P. mugo, P. uncinata, P. rotundata and P. uliginosa as revealed in needle sclerenchyma cells

The purpose of the present study was to test the taxonomic value of sclerenchyma in distinguishing Pinus sylvestris and P. mugo, P. uncinata, P. rotundata and P. uliginosa, all representing the subsection Sylvestres within the genus Pinus. Thirty-six samples were gathered in natural populations. Every sample was represented with 30 individuals, every individual with 10 brachyblasts. Three types of sclerenchymatic cells surrounding the resin canals and four between vascular bundles were distinguished. Relations among samples and taxa were verified using discriminant analysis and clustering based on Euclidean distances. The types of sclerenchymatic cells surrounding the resin canals and located between the vascular bundles differentiate the compared taxa when used as average frequencies but are extremely variable and do not allow the classification of every individual. The study demonstrated that the type of sclerenchymatic cells surrounding the resin canals and between the vascular bundles in needles could have an important taxonomic value in distinguishing the taxa of two-needle pines of the subsection Sylvestres in Europe at the population level. The distinguishing of individuals was difficult because of very high variation of sclerenchyma characters.     

Molecular analysis of two genes between let-653 and let-56 in the unc 22(IV) region of Caenorhabditis elegans

Summary A previous study of genomic organization described the identification of nine potential coding regions in 150 kb of genomic DNA from the unc-22(IV) region of Caenorhabditis elegans. In this study, we focus on the genomic organization of a small interval of 0.1 map unit bordered on the right by unc-22 and on the left by the left-hand breakpoints of the deficiencies sDf9, sDf19 and sDf65. This small interval at present contains a single mutagenically defined locus, the essential gene let-56. The cosmid C11F2 has previously been used to rescue let-56. Therefore, at least some of C11F2 must reside in the interval. In this paper, we report the characterization of two coding elements that reside on C11F2. Analysis of nucleotide sequence data obtained from cDNAs and cosmid subclones revealed that one of the coding elements closely resembles aromatic amino acid decarboxylases from several species. The other of these coding elements was found to closely resemble a human growth factor activatable Na⁺/H⁺ antiporter. Pairs of oligonucleotide primers, predicted from both coding elements, have been used in PCR experiments to position these coding elements between the left breakpoint of sDf19 and the left breakpoint of sDf65, between the essential genes let-653 and let-56.     

A molecular analysis of terminase cuts in headful packaging of Salmonella phage P22

Summary Fragments of DNA molecules of Salmonella phage 22 which represent the molecular termini created by the terminase reaction have been cloned and sequenced. The terminase cleavage separates a headful-sized piece of DNA from the concatemeric precursor; by successful cloning strategy it was shown that the terminase produces blunt ends. The termini of 20 different phage DNA molecules fall into a region located between about 600 and 4000 bp from the pac signal and show a Gaussian distribution. The average terminal redundancy was calculated to be about 2230 by (=5.3%) and is therefore higher than was previously reported. A comparison of the nucleotides flanking the terminal bases of 20 different end clones does not support the suggestion that the terminase recognizes some specific sequence and/or structural information in determining the actual cleavage site.     

Tn5 mutagenesis of Rhizobium trifolii host-specific nodulation genes result in mutants with altered host-range ability

Summary A 14 kb DNA fragment from the Sym plasmid of the Rhizobium trifolii strain ANU843, known to carry common nodulation nod and host specific nodulation hsn genes, was extensively mutagenised with transposon Tn5. A correlation between the site of Tn5 insertion and the induced nodulation defect led to the identification of three specific regions (designated I, II, III) which affected nodulation ability. Twenty-three Tn5 insertions into region I (ca. 3.5 kb) affected normal root hair curling ability and abolished infection thread formation. The resulting mutants were unable to nodulate all tested plant species. Tn5 insertions in regions II and III resulted in mutants which showed an exaggerated root hair curling (Hac⁺⁺) response on clover plants. Ten region II mutants which occurred over a 1.1 kb area showed a greatly reduced nodulation ability on clovers and produced aborted, truncated infection threads. Tn5 insertions into region III (ca. 1.5 kb) altered the outcome of crucial early plant recognition and infection steps by R. trifolii. Seven region III mutants displayed host-range properties which differed from the original parent strain. Region III mutants were able to induce marked root hair distortions, infection threads, and nodules on Pisum sativum including the recalcitrant Afghanistan variety. In addition region III mutants showed a poor nodulation ability on Trifolium repens even though the ability to induce infection threads was retained on this host. The altered host-range properties of region III mutants could only be revealed by mutation and the mutant phenotype was shown to be recessive.     

沙门氏菌检测技术研究进展

沙门氏菌(Salmonella)是一种常见的人畜共患病原菌,不仅能引起动物伤寒、霍乱,还会导致人类胃肠炎、败血症等疾病,严重威胁人、畜的生命健康,由其引起的食品安全事件高居所有食源性致病菌之首。食品中沙门氏菌的快速、准确检测是预防与控制沙门氏菌传播蔓延的重要手段。随着生物学、化学、物理等学科的快速发展,沙门氏菌的检测技术已从传统的分离培养和生化鉴定,发展到免疫学、分子生物学、电化学、传感器、生物芯片等快速、高通量检测,尤其是近年来与纳米技术、光谱学、质谱学以及代谢组学等的结合使用,为沙门氏菌快速、准确、灵敏的检测方法提供了新的发展方向。本文在参阅国内外最新研究报道的基础上,对各种方法进行总结阐述,并对沙门氏菌未来检测技术的发展动向予以分析。     

梅与山桃远缘杂交亲和性初步研究

为培育早花抗寒梅花新品种,以梅(Prunus mume)品种‘江梅’(P.mume‘Jiangmei’)、‘淡丰后’(P.mume‘Dan Fenghou’)与山桃(P.davidiana)、‘白花’山桃(P.davidiana‘Alba’)为亲本进行杂交试验,记录种间杂交结实率,观察花粉管生长,对未成熟胚进行培养。结果表明:(1)梅与山桃、‘白花’山桃杂交结实率很低,‘江梅’ב白花’山桃未结果,结实率最高的组合为‘淡丰后’×山桃,也仅有7.4%,且杂交果实的果核内部分胚干瘪、败育。(2)山桃和‘白花’山桃的花粉在梅柱头上都能正常萌发,但花粉管生长受抑制,多数花粉管到达花柱中部即弯曲、缠绕、断裂,花粉管生长过程中有大量的胼胝质产生,表现较低的杂交亲和性,但不同种间杂交亲和程度又有所不同。(3)通过未成熟胚培养获得了杂种苗。研究表明,梅与同属种杂交存在不亲和性,幼胚拯救是获得梅与李属其他种远缘杂交杂种苗的有效途径。