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The ultrastructure of twO kinds of transcription ally active chromatin, the lampbrush chromosome loops and the nucleoli from amphibian oocytes and primary nuclei of the green alga Acetabularia, has been examined after manual isolation and dispersion in low salt media of slightly alkaline pH using various electron microscopic staining techniques (positive staining, metal shadowing, negative staining, preparation on positively charged films, etc.) and compared with the appearance of chromatin from various somatic cells (hen erythrocytes, rat hepatocytes, ClIltured murine sarcoma cells) prepared in parallel. While typical nucleosomes were revealed with all the techniques for chromatin from the latter three cell system, no nucleosomes were identified in either the lampbrush chromosome structures or the nucleolar chromatin. Nucleosomal arrays were absent not only in maximally fibril-covered matrix units but also in fibril-free regions between transcriptional complexes, including the apparent spacer intercepts between different transcriptional units. Moreover, comparisons of the length of the repeating units of rDNA in the transcribed state with those determined in the isolated rDNA and with the lengths of the first stable product of rDNA transcription, the pre-rRNA, demonstrated that the transcribed rDNA was not significantly shortened and/or condensed but rather extended in the transcriptional units. Distinct granules of about nucleosomal size which were sometimes found in apparent spacer regions as well as within matrix units of reduced fibril density were shown not to represent nucleosomes since their number per spacer unit was not inversely correlated with the length of the specific unit and also on the basis of their resistance to treatment with the detergent Sarkosyl NL-30. It is possible to structurally distinguish between transcriptionally active chromatin in which the DNA is extended in a non-nucleosomal form of chromatin and condensed, inactive chromatin within the typical nucleosomal package. The characteristic extended structure of transcriptionally active chromatin is found not only in the transcribed genes but also in non-transcribed regions within or between ("spacer") transcriptional units as well as in transcriptional units that are untranscribed amidst transcribed ones and/or have been inactivated for relatively short time. It is hypothesized that activation of transcription involves a transition from a nucleosomal to an extended chromatin organisation and that this structural transition is not specific for single "activated" genes but may involve larger chromatin regions, including adjacent untranscribed intercepts.
No abstract available
In Fragebögen tauchen häufig ternäre Antwortmöglichkeiten auf (z.B. ja - nein - weiß nicht). Für eine Analyse solcher Hems werden Kennwerte vorgeschlagen. Dabei wird ein der Schwierigkeit analoger Popularitätsindex eingeführt, der in p+ den Anteil der Ja-Antworten angibt. Aus p+ und p-, dem Anteil der Nein-Antworten, wird ein Aktualitätsindex definiert, der in den Grenzen zwischen 0 und 1 variiert und die Eliminierung wenig aktueller Fragen gestattet. Zur Bestimmung der Trennschärfe werden Punkt-Vierfelder- oder phi-Koeffizienten angegeben. die aus der Zerlegung des X2 einer 3x2-Tafel in eine 2x2-Tafel und in eine auf die Unbestimmtheitsantwort zurückgehende Restkomponente entstehen. Ebenso werden Koeffizienten für Iteminterkorrelationen aus 3x3-Tafeln und Indizes für die Reliabilität angegeben.
The arrangement of transcriptional units in the loops of lampbrush chromosomes from oocyte nuclei of urodele amphibia and from primary nuclei of the green alga Acetabularia have been studied in the electron microscope using spread preparations. Loops with different patterns of arrangement of matrix units (i.e. to a first approximation, transcriptional units) can be distinguished: (i) loops consisting of one active transcriptional unit; (ii) loops containing one active transcriptional unit plus additional fibril-free, i.e. apparently untranscribed, intercepts that may include 'spacer' regions; (iii) loops containing two or more transcriptional units arranged in identical or changing polarities, with or without interspersed apparent spacer regions. Morphological details of the transcriptional complexes are described. The observations are not compatible with the concept that one loop reflects one and only one transcriptional unit but, rather, lead to a classification of loop types according to the arrangement of their transcriptional units. We propose that the lampbrush chromosome loop can represent a unit for the coordinate transcription of either one gene or a set of several (different) genes.
No abstract available
Derivatives A and B of the two sila-antihistam.ines silamephenhydramine and sila-chlorphenoxamine were synthesized for the first time by the steps shown in scheme 1. They and their precursors III and IV were characterized by their physical (Table 1) and chemical properties and their structures confirmed by NMR and mass spectroscopy (Tables 2 and 3). Their pharmacological effects were investigated and compared with those of the corresponding sila-antihistamines.
No abstract available
The disintegration of the nuclear envelope has been examined in nuclei and nuclear envelopes isolated from amphibian oocytes and rat liver tissue, using different electron microscope techniques (ultrathin sections and negatively or positively stained spread preparations). Various treatments were studied, including disruption by surface tension forces, very low salt concentrations, and non ionic detergents such as Triton X-lOO and Nonidet P-40. The high local stability of the cylinders of nonmembranous pore complex material is emphasized. As progressive disintegration occurred in the membrane regions, a network of fibrils became apparent which interconnects the pore complexes and is distinguished from the pore complexassociated intranuclear fibrils. This network might correspond to an indistinct lamella, about 15 - 20 nm thick, located at the level of the inner nuclear membrane, which is recognized in thin sections to bridge the interpore distances. With all disintegration treatments a somewhat higher susceptibility of the outer nuclear membrane is notable, but a selective removal does not take place. Final stages of disintegration are generally characterized by the absence of identifiable, membrane- like structures. Analysis of detergent-treated nuclei and nuclear membrane fractions shows almost complete absence of lipid components but retention of significant amount of glycoproteins with a typical endomembrane-type carbohydrate pattern. Various alternative interpretations of these observations are discussed. From the present observations and those of Aaronson and Blobel (1,2), we favor the notion that threadlike intrinsic membrane components are stabilized by their attachment to the pore complexes, and perhaps also to peripheral nuclear structures, and constitute a detergent-resistant, interpore skeleton meshwork.
No abstract available
The photoconductivity of both undeformed and deformed Te samples has been investigated at liquid He temperature by means of a Fourier spectrometer. Three peaks were usually found in the spectra of undeformed samples at 11, 24 and 46 cm\(^{-1}\). These are shown to be due to three different chemical impurities. The deformed samples are characterized by additional structure at higher frequencies.
The arrangement of genes of precursor molecules for ribosomal RNA (pre-rRNA) in primary nuclei from two green algae species, Acetabularia mediterranea and A. major, has been analyzed in an electron microscope study. The pattern of transcriptional units in individual strands of nucleolar chromatin was investigated using spread and positively stained preparations. The rDNA pattern is not uniform but differs in different strands. The predominant type of nucleolar chromatin exhibits a high degree of homogeneity in the sequence of matrix units (intercepts covered with fibrilst hat contain the pre-rRNA) and fibril-free spacer intercepts. Substantial differences, however, are observed between the patterns in different strands. In addition, there is evidence in some strands for intraaxial heterogeneity of both spacer and matrix units. The following major types can be distinguished: type la, ca. 2 micrometer long matrix units, extremely short spacer intercepts in A. mediterranea (ca. 1 micrometer long ones in A. major), completely homogeneous distribution; type Ib, as type la but with intercalated, isolated, significantly shorter and/or longer matrix units; type lIa, matrix unit sizes as in type la, but much longer spacer intercepts, high degree of homogeneity; type Ill, largely heterogeneous arrangements of matrix and spacer units of varying sizes. The matrix unit data are compared with the sizes of pre-rRNA as determined by polyacrylamide gelelectrophoresis under denaturing and non-denaturing conditions. The findings are discussed in relation to recent observations in amphibia and insects and with respect to current concepts of the species-specificity of rDNA arrangements.
Isoelectronic derivatives (A and B) and a homolog (C) of the two sila-antihistamines sila-clofenetamine and silamebrophenhydramine were synthesized for the first time by the steps shown in scheme 1. They and their unknown precursors II-IV were characterized by their physical (Table 1) and chemical properties and their structures confinned by lH-NMR and rnass spectroscopy (Tables 2 and 3). The pharrnacological effects of A and B were investigated and compared with those of the corresponding 0-isosteric sila-antihistarnines (Chapter 5).
Jahresbericht 1975
(1976)
Durch Umsetzungen von Alkalimetallcarbonaten mit Silber und Schwefel in der Schmelze wurden die ternären Sulfide K2Ag4S3 und Rb2Ag4S3 dargestellt. Röntgenographische Untersuchungen an Einkristallen führten zu einem neuen Schichtenstrukturtyp, in dem röhrenförmige Silber-Schwefel-Anordnungen mit nahezu trigonal planar von Schwefel koordinierten Silberatomen über gemeinsame S-Atome zu Schichten"verknüpft werden, zwischen denen die Alkalimetallatome eingelagert sind. Die monoklinen Elementarzellen enthalten vier Formeleinheiten. Die höchstsymmetrische Raumgruppe ist C2/m. Als Gitterkonstanten ergeben sich: K\(_2\)Ag\(_4\)S\(_3\): a = 17,36(1) A, b = 4,296(2) A, c = 11,603(5) A, B = 108,32(3t; Rb\(_2\)Ag\(_4\)S\(_3\): 80 = 17,88(1) A, b = 4,331(5) A, c = 11,849(5) A, B = 108,58(3)°.
No abstract available
No abstract available
Several types of "irregular" structures in the arrangement of lateral fibrils were noted in electron microscopic preparations of transcriptionally active nucleolar chromatin from various plant and animal cells. Such forms include: I. Disproportionately long lateral fibrils which occur either as individual fibrils or in groups; 2. "Prelude complexes" and other arrangements of lateral fibrils in apparent spacer intercepts; 3. Thickening of the rDNA chromatin axis at the starting end of pre-rRNA matrix units; 4. Extremely long matrix units , the length of which exceeds that of the rDNA (double-strand) sequence complementary to the specific pre-rRN A (for abbreviations see text). In addition, the stability of high molecular weight RNAs contained in the nucleolar ribonucleoproteins during the preparation for electron microscopy was demonstrated by gel electrophoresis. The observations indicate that the morphological starting point of a pre-rRNA matrix unit is not necessarily identical with the initiation site for synthesis of pre-rRNA, but they rather suggest that the start of the transcriptional unit is located at least O.2-D.8 JLm before the matrix unit and that parts of the "apparent spacer" are transcribed. It is proposed that the pre-rRN A molecules do not represent the primary product of rDNA transcription but rather relatively stable intermediate products that have already been processed during transcription.