Analysis of the time relationship for the interaction of X-ray induced primary breaks in the formation of dicentric chromosomes.

In split-dose experiments, the time relationship for the interaction of primary breaks in the formation of dicentric chromosomes was analysed. Human peripheral lymphocytes were irradiated with a dose of 340 R of 220 kV X-rays split into two equal fractions separated by intervals up to 360 min. Assuming an exponential decline of the time-dependent quadratic component of the dose realtion of dicentrics a theoretical formula was deduced. Fitting this formula to the empirical data a mean time of 110 min could be calculated in which primary breaks induced by both dose-fractions can interact to form dicentric chromosomes.     

Fragility and spiralization anomalies of the chromosomes in three cases, including fraternal twins, with Fanconi's anemia, type Estren-Dameshek

Fraternal twins, offspring of consanguineous parents, developed pancytopenia, the boy at 7, the girl at 12 years of age. A third patient became anemic at 3 years. All three are free of associated malformations. In blood cultures the incidence of chromatid breaks, exchanges, and chromosome-type aberrations was elevated to 24%, 18%, and 28%, respectively. In addition, in a low number of mitotic cells unusual observations, pointing to profound disturbances of chromosome structure, were made. It is suggested that these patients have a genetic defect impairing the normal process of mitotic chromosome condensation and decondensation.     

Tonnacypris glacialis (Ostracoda, Cyprididae): taxonomic position, (palaeo-) ecology, and zoogeography

Abstract. The freshwater ostracod Tonnacypris glacialis (Sars, 1890) is reported from the European Pleistocene for the first time. The historical allocation of the species is discussed, and the species composition and characteristics of Tonnacypris Diebel & Pietrzeniuk (1975) and its phylozoogeography are considered. The significance of T. glacialis is reviewed, particularly from the viewpoint of the possible implications of parthenogenesis (and occasional-male production) for the Quaternary history of the genus, and for the use of the species in palaeoenvironmental reconstruction. It is suggested that the Pleistocene fossil occurrence of T. glacialis in modern temperature latitudes is a robust indicator of mean summer temperatures of 6°C.     

Site of synthesis of geranylgeraniol derivatives in intact spinach chloroplasts

Chloroplasts isolated from fully developed spinach leaves and incubated in the presence of isopentenyl pyrophosphate were able to synthesize rapidly geranylgeranyl chlorophyll a and geranylgeraniol.The biosynthesis of the geranylgeraniol derivatives from isopentenyl pyrophosphate is a compartimentalized process. The membrane fractions (thylakoid and envelope membranes) were essentially unable to synthesize geranylgeraniol, geranylgeranyl pyrophosphate and geranylgeranyl chlorophyll a. When stromal and thylakoid fractions were combined the capacity to synthesize geranylgeranyl chlorophyll a and geranylgeraniol was restored. When stromal and envelope membrane fractions were combined the capacity to synthesize geranylgeranyl pyrophosphate and geranylgeraniol was restored. The products of the reaction were discharged inside the lipid phase of the membranes.     

The structure of bovine carboxypeptidase B: results at 5-5 Angstrom resolution

We have used rotation and translation search methods to determine whether bovine Carboxypeptidase A and Carboxypeptidase B have similar tertiary conformations.Our results show that, at 5·5 Å resolution, the two enzymes are indeed similar in structure. Difference Fourier synthesis reveals features of Carboxypeptidase B that correlate with known differences between the two proteins.     

Biochemical and cytogenetic studies on the Nucleolus Organizing Regions (NOR) of Man

Summary The hybridization kinetics of DNA with labeled (18s+28s)rRNA from HeLa cells was determined in patients with trisomy 21, healthy probands with normal karyotype and in carriers of a t(DqGq) centric fusion. The results are in, accordance with the saturation values obtained earlier for these probands:Three patients with trisomy 21 showed an increased saturation level. In 2 of these patients the excess of rDNA exceeded the expected value considerably.Three of the investigated translocation carriers t(14q21q) showed significantly reduced saturation values, while results of a fourth proband with a dicentric chromosome t(15q21q) were found to be within the range of normal probands.The heterogeneous results were correlated with the cytogenetic characteristics of the acrocentric chromosomes. It is expected that these differences could be explained on the basis of family analysis.

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Zusammenfassung Hybridisierungskinetiken der DNA mit markierter (18s+28s)rRNA aus HeLa-Zellen wurden ermittelt bei Patienten mit Trisomie 21, gesunden Probanden mit normalem Karyotyp und Trägern einer zentrischen Fusion t(DqGq). Die Ergebnisse bestätigen die bereits früher ermittelten Sättigungswerte von Hybridisierungen bei diesen Probanden:3 Patienten mit Trisomie 21 zeigten erhöhte Sättigungsniveaus. Bei 2 dieser Patienten übersteigt der Überschuß an rDNA den Erwartungswert erheblich.3 der untersuchten Translokationsträger t(14q21q) hatten signifikant erniedrigte Sättigungswerte, während die vierte Probandin mit dem dizentrischen Chromosom t(15q21q) im Normbereich lag.Die unterschiedlichen Befunde werden mit den cytogenetischen Eigenschaften der akrozentrischen Chromosomen in Zusammenhang gebracht. Es wird erwartet, daß diese Unterschiede sich durch Familienuntersuchungen aufklären lassen.