The intrinsically disordered amino-terminal region of human RecQL4: multiple DNA-binding domains confer annealing,strand exchange and G4 DNA binding

Human RecQL4 belongs to the ubiquitous RecQ helicase family. Its N-terminal region represents the only homologue of the essential DNA replication initiation factor Sld2 of Saccharomyces cerevisiae, and also participates in the vertebrate initiation of DNA replication. Here, we utilized a random screen to identify N-terminal fragments of human RecQL4 that could be stably expressed in and purified from Escherichia coli. Biophysical characterization of these fragments revealed that the Sld2 homologous RecQL4 N-terminal domain carries large intrinsically disordered regions. The N-terminal fragments were sufficient for the strong annealing activity of RecQL4. Moreover, this activity appeared to be the basis for an ATP-independent strand exchange activity. Both activities relied on multiple DNA-binding sites with affinities to single-stranded, double-stranded and Y-structured DNA. Finally, we found a remarkable affinity of the N-terminus for guanine quadruplex (G4) DNA, exceeding the affinities for other DNA structures by at least 60-fold. Together, these findings suggest that the DNA interactions mediated by the N-terminal region of human RecQL4 represent a central function at the replication fork. The presented data may also provide a mechanistic explanation for the role of elements with a G4-forming propensity identified in the vicinity of vertebrate origins of DNA replication.     

Biodiversity in a complex world: consolidation and progress in functional biodiversity research

The global decline of biodiversity caused by human domination of ecosystems worldwide is supposed to alter important process rates and state variables in these ecosystems. However, there is considerable debate on the prevalence and importance of biodiversity effects on ecosystem function (BDEF). Here, we argue that much of the debate stems from two major shortcomings. First, most studies do not directly link the traits leading to increased or decreased function to the traits needed for species coexistence and dominance. We argue that implementing a trait-based approach and broadening the perception of diversity to include trait dissimilarity or trait divergence will result in more realistic predictions on the consequences of altered biodiversity. Second, the empirical and theoretical studies do not reflect the complexity of natural ecosystems, which makes it difficult to transfer the results to natural situations of species loss. We review how different aspects of complexity (trophic structure, multifunctionality, spatial or temporal heterogeneity, and spatial population dynamics) alter our perception of BDEF. We propose future research avenues concisely testing whether acknowledging this complexity will strengthen the observed biodiversity effects. Finally, we propose that a major future task is to disentangle biodiversity effects on ecosystem function from direct changes in function due to human alterations of abiotic constraints.     

Preferential X inactivation in human placenta membranes: Is the paternal X inactive in early embryonic development of female mammals?

Summary In placenta membranes of newborn girls carrying electrophoretically distinguishable G6PD alleles, the maternally derived isozyme is expressed preferentially. This phenomenon cannot be explained by allelic differences in enzyme activity or by somatic selection directed against cells with particular G6PD phenotypes. Instead, it may be that in this tissue X inactivation is nonrandom. Preferential expression of the maternal X chromosome, as has been shown in marsupials and in extraembryonic membranes of rodents and now in man, may reflect the state of activity of the X chromosomes in the early stages of female embryonic development.H.-H. R. is supported by the Deutsche Forschungsgemeinschaft     

Synchronization of Dunaliella cultures

Summary Dunaliella cells exhibit different temperature optima for photosynthesis and cell division. Using this observation a combined light-dark and highlow temperature treatment is given to synchronize cell suspensions.     

A novel labeling procedure of anteiso-fatty acid-containing lipids in staphylococci for investigating the effect of penicillin on lipid release

L-[4,5-3H]isoleucine was introduced to label anteiso-fatty acid (AIFA)-containing lipids in Staphylococcus aureus SG 511. After an overnight incubation in peptone broth in the presence of 37 kBq L-[4,5-3H]isoleucine/ml, 8.5-13% of the total radioactivity applied was found to be incorporated into the cells. 22.4-25.6% of the incorporated radioactivity was found in AIFA-containing lipids extracted by chloroform-methanol-water (2:1:0.2, v/v/v) at pH 2. The interphase contained 70-75% of the incorporated radioactivity. Lipoteichoic acid, extracted by phenol-water (80:20, w/v) contained less than 1% of the incorporated radioactivity, as measured after purification by hydrophobic interaction chromatography on octyl sepharose gel. Within 1 h after addition of 10 micrograms/ml penicillin G to exponentially growing cultures of S. aureus, that led to non-lytic death of the cells, 11.9-18.1% of the incorporated L-[4,5-3H]isoleucine label were released. Lipids containing AIFA were excreted to 5.4-8.4% of total incorporated activity; this amount represents more than 1/4 of the labeled cellular lipids.     

Über das Reaktionsspektrum von Rezeptoren aus der Riechschleimhaut von Wasserfröschen (Rana esculenta)

Zusammenfassung Aus dem Riechepithel von Rana esculenta wurden mit metallgefüllten Mikropipetten Aktionspotentiale einzelner Rezeptoren abgeleitet (Dauer 4–7 msec, maximale Frequenz 10 Imp./sec). Die Reaktionen von 25 Zellen auf 28 Duftstoffe werden beschrieben.Fast alle daraufhin geprüften Zellen reagieren auf Oenanthaldehyd, Amylacetat, Capronsäureäthylester und Caprylsäureäthylester mit einer Erhöhung der Impulsfrequenz (Grundspektrum). Außerdem haben die Rezeptoren ein variables Beispektrum geringen Umfanges.

---

Odor specificities of receptors in the olfactory epithelium of the frog Rana esculenta

Summary Action potentials from single receptors in the olfactory epithelium of water frogs (Rana esculenta) have been recorded by means of metal filled glass pipettes. The reactions of 25 cells to stimulation with 28 odorous substances are described. All cells so far tested showed an increase in spike frequency when stimulated with heptanal, amyl acetate, the ethyl ester of hexanoic acid, and the ethyl ester of octanoic acid, (basic spectrum). An additional small but variable reaction spectrum (side spectrum) was recorded.

---

---

Herrn Prof. Dr. H. Autrum zum 60. Geburtstag gewidmet.