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2.
Evidence that the normal route of replication-allowed Red-mediated recombination involves double-chain ends. 总被引:9,自引:0,他引:9 下载免费PDF全文
Recombination mediated by the Red pathway of bacteriophage lambda is focused towards sites of double-chain cuts. Double-chain ends created either by type II restriction enzymes acting at unmodified recognition sites or by lambda's packaging enzyme, terminase, acting at cos are utilized in a manner similar to the double-chain break repair pathway of recombination in yeast. When lambda is allowed to recombine during replicative growth, spontaneous recombination is approximately evenly distributed along the chromosome. It has been proposed that replication-allowed recombination also is initiated by double-chain ends. In order to test this hypothesis we ask if the in vivo expression of the Mu gam protein is inhibitory to Red recombination. Mu gam has been shown in vitro to bind to linearized duplex DNA and to shield bound DNA from exonucleases. The expression of Mu gam is found to be inhibitory to Red recombination whether replication is blocked or allowed. As a control we ask if Mu gam inhibits Int-mediated recombination. It has been well documented that the Int pathway of recombination does not involve any double-chain breaks and, consistent with this, the Int pathway is not inhibited by Mu gam. We suggest that the in vivo expression of Mu gam or other similar activities may be a generally useful way to determine if those processes that respond to an artificially introduced double-chain cut normally involve double-chain ends. 相似文献
3.
J. Le Dérout David S. Thaler † Nancy Guillén‡ Luisa Hirschbein 《Molecular microbiology》1992,6(11):1495-1505
Bacillus subtilis can exist in a diploid state in which two genetically distinct chromosomes co-exist in the same cell and yet only one of them is expressed, thereby determining the phenotype. Such cells are called non-complementing diploids (Ncds). In this study, two types of experiments are reported which indicate that a previously known pleiotropic gene, spo0A, plays a role in the maintaining the diploid state, as follows. (i) When protoplasts of two Spo0A mutant strains were fused, the resulting products continued to segregate cells of both parental phenotypes for many more divisions than had been reported previously. (ii) When a stable Ncd (an Ncd in which the unexpressed markers are not spontaneously activated at a detectable level) harbouring a chloramphenicol acetyltransferase gene on the silent chromosome was transformed with spo0A null alleles the transformants often expressed chloramphenicol acetyltransferase activity. Together these results indicate that the spo0A gene is involved in maintenance of the diploid state in both unstable and stable Ncds. 相似文献
4.
H-2 Polymorphisms Are More Uniformly Distributed than Allozyme Polymorphisms in Natural Populations of House Mice 下载免费PDF全文
Patterns of H-2 and allozyme polymorphism in natural populations of house mice from Europe, North Africa and South America were analyzed. The purpose of the analysis was to determine whether H-2 and allozyme polymorphisms were similarly distributed both geographically and temporally in wild mice. Two subspecies of house mice, Mus musculus domesticus and M. m. musculus were sampled and the polymorphisms of two H-2 class I genes, H-2K and H-2D, and 34 allozyme-encoding genes were surveyed. The three kinds of analyses that were conducted included a hierarchical gene diversity analysis, an analysis of the effects of barriers to gene flow, and an analysis of similarity networks. Each of the comparisons demonstrated that H-2 polymorphisms were more uniformly distributed than allozyme polymorphisms and provided additional evidence that H-2 and allozyme polymorphisms are subject to different evolutionary pressures. The analysis of similarity networks also demonstrated that H-2 genes provide little information about the phylogeny of wild mice. 相似文献
5.
Zusammenfassung EinAesculus-Baum, der sich im Frühling alljährlich vorzeitig belaubt, entlaubt sich im Herbst auffallend spät. Die Knospen dieses Baumes haben eine sehr kurze freiwillige Winterruhe, bei günstigen Temperaturen treiben sie bereits Mitte Dezember aus, ein Warmbad verzögert das Austreiben. Die frühtreibenden Kastanien sind durch Spätfröste, ja selbst durch Winterfröste gefährdet, denn ihre vorzeitig in Saft stehenden Knospen und Triebe fallen dem Frost leichter zum Opfer als diejenigen der länger ruhenden Bäume.Herrn Prof. Dr. H. v.Guttenberg zum 80. Geburtstag gewidmet. 相似文献
6.
Richard Karban Gregory English-Loeb M. Andrew Walker Jennifer Thaler 《Experimental & applied acarology》1995,19(4):189-197
We observed the number of predatory mites (Phytoseiidae:Typhlodromus caudiglans) on the foliage of 20 North American species of grapes (Vitis spp) plus the domesticated EuropeanVitis vinifera, all grown in a common garden. We found relatively few phytophagous mites. The numbers of phytophagous mites were not correlated with the plant characteristics that we measured. We found approximately five times as many predatory mites as phytophagous mites and the numbers of these phytoseiid predators were not affected by the availability of prey. Similarly, numbers of phytoseiids were unaffected by plant gender and, hence, the availability of pollen, another source of food. The numbers of phytoseiids were not clustered according to the taxonomic grouping of the tested plant species. Leaf surface characteristics explained over 25% of the variance in the numbers of phytoseiids. Numbers of phytoseiids were positively associated with the density of vein hairs, the density of bristles in leaf axils, and the presence of leaf domatia. These results suggest that sheltered habitats rather than food availability may limit the numbers of phytoseiid mites on grapevines. 相似文献
7.
Purification and characterization of xenorhabdicin, a phage tail-like bacteriocin, from the lysogenic strain F1 of Xenorhabdus nematophilus. 总被引:2,自引:0,他引:2 下载免费PDF全文
Xenorhabdicin, the phage tail-like bacteriocins of Xenorhabdus nematophilus, and phage head particles, elements produced together after mitomycin induction in X. nematophilus lysogenic strain F1 cultures, were separated by DEAE chromatography, examined by transmission electron microscopy, and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Electrophoresis of xenorhabdicin showed two major subunits of 43 and 20 kDa corresponding to the sheath and the inner core, respectively. At least five other minor subunits of 67, 54, 35, 28, and 16 kDa were also characterized. Electrophoresis of the phage head capsids showed a major 40-kDa subunit and two minor 50- and 34-kDa subunits. Bactericidal activity recorded against closely related bacterial species and spontaneously produced by X. nematophilus resides in the xenorhabdicin particles and is another antimicrobial barrier to save the symbiotic association. 相似文献
8.
Tapas K. Makar Dr. Arthur J. L. Cooper Beth Tofel-Grehl Howard T. Thaler John P. Blass 《Neurochemical research》1995,20(6):705-711
Glutathione and total carnitine (i.e., free carnitine plus acid-soluble carnitine esters) were measured in an affected (superior frontal gyrus; SFG) and unaffected (cerebellum: CBL) region of Alzheimer disease (AD) and control brains. Average glutathione content in AD SFG (n=13) and AD CBL (n=7) (7.9±2.1 and 11.9±4.0 nmol/mg protein, respectively (mean ±S.D.)) was similar to that in control SFG (n=13) and CBL (n=6) (7.7±2.0 and 11.6±2.6 nmol/mg protein, respectively). However, glutathione increased significantly with age in AD brain (p=0.003) but not in control brain. Average total carnitine in AD SFG (84±47 pmol/mg protein; n=10) and AD CBL (108±86 pmol/mg protein; n=7) was not significantly different from that in the corresponding regions of control brain (148±97 (n=10) and 144±107 (n=6) pmol/mg protein, respectively). However, a significant decline of total carnitine with age in both regions was noted for AD brain, but not for control brain. Carnitine acetyltransferase activity in the AD SFG (n=13) was not significantly different from that of control SFG (n=13) (1.83±1.05 and 2.04±0.82 nmol/min/mg protein, respectively). However, carnitine acetyltransferase activity of AD CBL (n=7) was significantly lower than that of control CBL (n=6) (1.33±0.88 versus 2.26±0.66 nmol/min/mg protein; p=0.05). 相似文献
9.
Unbalanced growth induced by depletion of manganese ions was a prerequisite for production of ribonucleotides in a high salt mineral medium with the wildtype strain Brevibacterium ammoniagenes ATCC 6872. The concentration of manganese strictly controlled the overall deoxyribonucleic acid (DNA) synthesis, whereas ribonucleic acid (RNA), protein and cell wall synthesis remained essentially unimpaired in the manganese-lacking cells.The reversibility of inhibition of overall DNA synthesis was shown by enhanced incorporation (up to threefold compared to the cultures supplied with sufficient manganese) of [8-14C] adenine into alkali-stable, trichloroacetic acid-insoluble material after subsequent addition of 10 M MnCl2 to 15 h-old depleted cultures.The results of inhibitor studies on the restoration of overall DNA synthesis due to subsequent addition of manganese ions to depleted cultures suggest that ribonucleotide reduction is the primary target of the manganese starvation during nucleotide fermentation with Brevibacterium ammoniagenes ATCC 6872. 相似文献
10.
Zusammenfassung Der Waldrapp verfügt als soziale Vogelart über Verhaltensweisen des Gruppen- wie Paarkontaktes, die durch Veränderung von Körperumriß und Färbung unbefiederter Hautstellen verstärkt werden können: Grüßen, Imponieren, Aggressivverhalten (auch bei Nestlingen), Beschwichtigen, soziale Körperpflege, Kopula, Nestbau-Verhalten, Paarsitzen. Für das Zusammenspiel der Kolonie wichtig sind Grüßen, verschiedene Formen des Imponierens und ritualisierte Aggressionshandlungen. Das Fortpflanzungsgeschehen synchronisieren soziale Gefiederpflege, Kopulationen (bzw. Scheinkopulae) und Nestbauhandlungen. Das Paarsitzen, besonders deutlich außerhalb der Brutperiode, zeigt vermutlich Monogamie an.Das Lautrepertoire, eintönig für das menschliche Ohr, ist individuell variabel.Eine Besonderheit der Waldrappe ist auch die Nestlings-Aggressivität. Nestgeschwister trachten, einander durch Schnabelhiebe in eine Beschwichtigungshaltung zu drängen und so am Betteln zu hindern. Das Verhalten erlischt bei Erreichen eines Gewichtes von ca. 800 g, zugleich mit dem Abflachen der Wachstumskurve. Da Waldrappe ab dem ersten Ei brüten, überleben untergewichtige Letztgeschlüpfte (Nesthäkchen) bei ausreichendem Nahrungsangebot aufgrund ihrer länger anhaltenden Aggressivität.
Social behaviour of the Bald IbisGeronticus eremita — observations at the Alpenzoo, Innsbruck
Summary As a social bird the Bald Ibis shows behaviour patterns for group contact as well as for pair contact: greeting, display, aggressive behaviour of adults and sibling competition, appeasement behaviour, social preening, nesting behaviour, and Paarsitzen (spatial bond). Some of them may be reinforced by changing body-shape and colour of unfeathered skin. Greeting, some forms of display and ritualized aggressions are important for normal intraspecific interactions. Social preening, copulations (false copulae also) and nesting behaviour do not only stimulate the partner, they also synchronize activity within a colony. Paarsitzen might indicate longer lasting monogamy. The vocal inventory is rather uniform, but some calls may vary individually. — The Bald Ibis shows a strong sibling competition. Siblings force to prevent each other to gape by violent pecking and thus releasing appeasement behaviour. Sibling competition stops with about 800 g at the end of the period of rapid body growth. As the Bald Ibis is breeding with the first egg, this behaviour may allow survival of the runt because of its longer lasting aggressivity when there is sufficient food supply.相似文献