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A specific class of DNA sequences, the inverted repetitive sequences, forms a double-stranded structure within a single linear polynucleotide chain in denatured DNA. The reassociation process is unimolecular and occurs very fast. Quantitative analyses have shown that these sequences com-E rise about 4-5% of the nuclear DNA of various mammalian cells (P815 mouse mastocytoma, Hela, L cells, Raji and Chang cells, and human embryonic hepatocytes) and are interspersed within sequences of other degrees of repetitiveness.
After labeling the cells with L-[Metnyl-3H]methionine and [14C]deoxycytidine, relative rates of enzymic DNA methylation were computed on the basis of 3H and 14C radioactivities found in py rimidine residues of the nuclear DNA. The results indicate that DNA of inverted repetitive sequences is methylated to a level about 50% higher than the ordinary repetitive sequences and to about 300% higher than the unique and intermediary sequences.
The biological function of the inverted repeats as well as the role of their enzymic hypermethyl ation is unknown.
The sequence complexity of nuclear RNA from mouse liver, mouse spleen and highly malignant P815 mastocytoma was measured by nRNA driven hybridization to unique DNA sequences of P815 cells. The unique DNA sequences represent 63% of the total nuclear DNA of P815 cells and their availibility in hybridization experiments was found to be 76%. Of these sequences 7.8% formed hybrids with nuclear RNA of this cell, about 11.5% with mouse spleen and about 14.5% with mouse liver nuclear RNA. Assuming an asymmetrical transcription, the complexities of these transcripts are 2.8 × 108 nucleotides for mouse P815 mastocytoma, 4.3 × 108 for mouse spleen and about 5.3 × 108 nucleotides for mouse liver.
Cellular specifity of the transcribed information was analyzed in additivity experiments, in which unique DNA sequences, not complementary to the nuclear RNA of one cell were annealed to the nuclear RNAs of the two other tissues/cells. In these experiments most of the nuclear RNA se quences of P815 cells were found to be also present in the nucleus of mouse liver and spleen. Only a small portion of the unique DNA sequences of P815 mastocytoma (about 1.2% corresponding to 4.4 ×107 nucleotides) was found to be complementary only to P815 mastocytoma nuclear RNA.
The isolation of transcribed DNA sequences of P815 cells and the partial characterization with respect to their sequence composition and relative rates of enzymatic DNA methylation are reported in this paper. Transcribed regions were purified by affinity chromatography using immobilized heterogenous nuclear RNA of P815 cells. About 10% of total genome was found in this fraction. Reassociation analyses showed differences in sequence composition of transcribed versus non-transcribed DNA fractions. The relative proportion of inverted repeats was doubled in the transcribed fraction whereas ordinary highly repetitive sequences comprising mainly of satellite DNA were found almost exclusively in the non-transcribed regions of the P815 genome. About 70% of transcribed portions corresponds to unique and intermediary DNA sequences. After labelling of cells with L-[Methyl-3H]methionine and [14C]deoxycytidine relative rates of enzymatic DNA methylation were computed for different kinetic components of transcribed and non- transcribed portions of P815 genome. No difference was found except in inverted repeats. In transcribed DNA the relative rate of enzymatic DNA methylation was only about 40% of that of the non-transcribed ones. We have quantitated this hypomethylation and found that there is, in average, about one 5-methylcytosine residue in 100 nucleotides of transcribed inverted repeats, compared to about 2.5 5-methylcytosines in non-transcribed fractions. In view of these data we propose that the enzymatic methylation of inverted DNA repeats negatively controls the transcriptional process in a given genomic region.
Book Review: This volume is the proceedings of an international conference on the evolution and phylogeny of Orthopteroidea, held in Siena, Italy, January 1986. The occasion for the conference was the 90th birthday of Dr. Felice Capra, of the Museo di Storia Nutrale di Genova. The proceedings consist of 53 papers, in English, ranging in length from 111 pages (Baccetti) to less than one page of text (Carlberg). Their subject matter is similarly diverse - as one would expect if more than 50 orthopterists were invited to give papers at a conference of this title.
In der vorliegenden Arbeit werden Bestände vorwiegend aus dem Raum Köln-Aachen beschrieben, in denen die sehr expansive, neophytische Art Senecio inaequidens DC. an ruderalen oder ruderalisierten Standorten meist schon häufiger auftritt. Die ca. 160 vorgestellten Vegetationsaufnahmen zeigen in ihrer Zuordnung zu bestimmten Pflanzengesellschaften ein breites Spektrum von den Sedo-Scleranthetea, Chenopodietea (Sisymbrion), Artemisietea (Dauco-Melilotion), Molinio-Arrhenatheretea (Arrhenatherion), Plantaginetea (Polygonion avicularis), Agropyretea (Convolvulo-Agropyrion), Agrostietea (Agropyro-Rumicion) über Bidentetea und andere Feuchtgesellschaften hin zum Sambuco-Salicion capreae bzw. Salicion albae. Sonderformen unterschiedlichster Standortbedingungen werden zusätzlich angeführt. Obwohl das Optimum der Art im Dauco-Melilotion an warm-trockenen Standorten zu liegen scheint, bleiben solche unter anderen edaphischen Bedingungen nicht ausgeschlossen. Soziologisch ungesättigte Gesellschaften und ihre Entwicklungsphasen an anthropogen gestörten bzw. geschaffenen Standorten werden bevorzugt besiedelt. Angaben über Herkunft, Verbreitung und Ökologie der Art, die in Bremen und seinem Umland sowie im Raum Aachen-Köln-Düsseldorf als eingebürgert zu gelten hat, ergänzen die Gesamtdarstellung.
The NA35 experiment has collected a high statistics set of momentum analyzed negative hadrons near and forward of midrapidity for central collisions of 200A GeV/c 32S+S, Cu, Ag, and Au. Using momentum space correlations to study the size of the source of particle production, the transverse source radii are found to decrease by ~40% at midrapidity and ~20% at forward rapidity while the longitudinal radius RL is found to decrease by ~50% as pT increases over the interval 50<pT<600 MeV/c. Calculations using a microscopic phase space approach (relativistic quantum molecular dynamics) reproduce the observed trends of the data. PACS: 25.75.+r
Any book that purports to be an encyclopedic treatment of the behavior of insects, arachnids, myriapods, and terrestrial representatives of other invertebrate phyla invites skepticism. That made it all the more pleasing to find this book to be remarkably comprehensive and scholarly. Adding to this pleasure were more than 200 full-color, original photographs of live invertebrates doing what land animals do and about 40 line illustrations redrawn from the primary literature.
The directed and elliptic flow of protons and charged pions has been observed from the semi-central collisions of a 158 GeV/nucleon Pb beam with a Pb target. The rapidity and transverse momentum dependence of the flow has been measured. The directed flow of the pions is opposite to that of the protons but both exhibit negative flow at low pt. The elliptic flow of both is fairly independent of rapidity but rises with pt. PACS numbers: 25.75.-q, 25.75.Ld
Using the NA49 main TPC, the central production of hyperons has been measured in CERN SPS Pb - Pb collisions at 158 GeV c-1. The preliminary ratio, studied at 2.0 < y < 2.6 and 1 < pT < 3 GeV c-1, equals ~ (13 ± 4)% (systematic error only). It is compatible, within errors, with the previously obtained ratios for central S + S [1], S + W [2], and S + Au [3] collisions. The fit to the transverse momentum distribution resulted in an inverse slope parameter T of 297 MeV. At this level of statistics we do not see any noticeable enhancement of hyperon production with the increased volume (and, possibly, degree of equilibration) of the system from S + S to Pb + Pb. This result is unexpected and counterintuitive, and should be further investigated. If confirmed, it will have a significant impact on our understanding of mechanisms leading to the enhanced strangeness production in heavy-ion collisions.