High light exposure leads to a sign change in gravitaxis of the flagellate Euglena gracilis

In the absence of other external stimuli the motile, unicellular freshwater flagellate Euglena gracilis normally swims upward in the water column (negative gravitaxis). This behavior is most likely triggered by active physiological orientation mechanisms. Recently it was found that negative gravitaxis often inverts to a positive one upon high light exposure. This response is not mediated by the photoreceptor (the paraxonemal body - PAB), because PAB-free mutants do also show this response after high radiation. It is very likely that the phenomenon is triggered by reactive oxygen species, because in the absence of oxygen no gravitaxis sign change was observed. Also increased salinity inverses the sign of gravitaxis, leading to the assumption that environmental stressors induce the formation of reactive oxygen species, serving as signal molecules.     

Identification of two mosquitocidal Bacillus cereus strains showing different host ranges

Mosquitocidal bacteria, M413 and C32 have been isolated from sediment samples collected from woodland and ditch, respectively. Gas chromatographic analysis of fatty acids methyl esters (GC-FAME) and 16S rRNA gene sequence alignment results showed these isolates belong to Bacillus cereus. The SDS-PAGE analysis of sporulated cultures of both isolates showed two major bands very similar in size. Interestingly, however, M413 is mainly toxic to 4th instars of Ochlerotatus taeniorhynchus whereas C32 is to those of Culex quinquefasciatus.     

A new genus and a new species of tachinids (Diptera,Tachinidae) from Wrangel Island

Aesia gen. n. with the type species Aesia acerbiana sp. n. is described from Wrangel Island. The new genus belongs to the tribe Blondeliini (as indicated by a short prealar bristle of the mesonotum and by the cerci separated in apical 0.4). It is not similar to any Palaearctic genus of tachinids. In the key to the species of Blondeliini of North and Central America and the West Indies it comes to the genus Eucelatoria but differs from it in having eyes covered with long and dense hairs, the lower facial margin protruding forwards and well visible in lateral view, proboscis with elongate prementum, abdomen of the female not modified, without a keel and piercer. Aesia acerbiana sp. n. was reared from a larva of a tiger moth (Arctiidae), Acerbia alpina Quensel collected in the tundra landscape.     

Zur Heredität des Strabismus concomitans

697 children with concomitant strabism, all patients who were seen in the Ophthalmalogical university hospital and outpatient service of the Charité, Berlin, during a certain period, have been examined together with their parents and siblings. In a second series, 3398 12-years old school children (born 1953) from three urban districts of Berlin were examined at the occasion of a vaccination term, and 179 children with strabism were ascertained. Probands as well as their parents and siblings were examined thoroughly according to the criteria of strabism diagnostics. Incidence of squinting among siblings was increased markedly when compared with the population frequency, but did not reach the expectations under rthe assumption of a single, monomeric mode of inheritance. Admixture of phenocopies or new mutants could be excluded. Twin investigations (12 monocygotic and 27 dicygotic pairs) showed a manifestation rate of 94,1% in monocygotic pairs, corresponding to a 3 1/2 times higher concordance in monocygotic as compared with dicygotic twins. From the results discussed, a multifactorial genetic system in combination with a threshold effect seems to be the most likely genetic interpretation. An analysis of pedigrees shows that slight sensoric as well as motoric anomalies might combine in different and continuously varying quantities, contributing to the syndrom of concomitant strabism.     

EPR, ENDOR, and TRIPLE resonance spectroscopy on the neutral flavin radical in Escherichia coli DNA photolyase

Ultraviolet radiation promotes the formation of a cyclobutane ring between adjacent pyrimidine residues on the same DNA strand to form a pyrimidine dimer. Such dimers may be restored to their monomeric forms through the action of a light-absorbing enzyme named DNA photolyase. The redox-active cofactor involved in the light-induced electron transfer reactions of DNA repair and enzyme photoactivation is a noncovalently bound FAD. In this paper, the FAD cofactor of Escherichia coli DNA photolyase was characterized as the neutral flavin semiquinone by EPR spectroscopy at 9.68 and 94.5 GHz. From the high-frequency/high-field EPR spectrum, the principal values of the axially symmetric g-matrix of FADH(*) were extracted. Both EPR spectra show an emerging hyperfine splitting of 0.85 mT that could be assigned to the isotropic hyperfine coupling constant (hfc) of the proton at N(5). To obtain more information about the electron spin density distribution ENDOR and TRIPLE resonance spectroscopies were applied. All major proton hfc's could be measured and unambiguously assigned to molecular positions at the isoalloxazin moiety of FAD. The isotropic hfc's of the protons at C(8alpha) and C(6) are among the smallest values reported for protein-bound neutral flavin semiquinones so far, suggesting a highly restricted delocalization of the unpaired electron spin on the isoalloxazin moiety. Two further hfc's have been detected and assigned to the inequivalent protons at C(1'). Some conclusions about the geometrical arrangement of the ribityl side chain with respect to the isoalloxazin ring could be drawn: Assuming tetrahedral angles at C(1') the dihedral angle between the C(1')-C(2') bond and the 2p(z)() orbital at N(10) has been estimated to be 170.4 degrees +/- 1 degrees.     

Kinetics control preferential heterodimer formation of platelet-derived growth factor from unfolded A- and B-chains

The folding and assembly of platelet-derived growth factor (PDGF), a potent mitogen involved in wound-healing processes and member of the cystine knot growth factor family, was studied. The kinetics of the formation of disulfide-bonded dimers were investigated under redox reshuffling conditions starting either from unfolded and reduced PDGF-A- or B-chains or an equimolar mixture of both chains. It is shown that in all cases the formation of disulfide-bonded dimers is a very slow process occurring in the time scale of hours with a first-order rate-determining step. The formation of disulfide-bonded PDGF-AA or PDGF-BB homodimers displayed identical kinetics, indicating that both monomeric forms as well as the dimerized homodimer have similar folding and assembly pathways. In contrast, the formation of the heterodimer occurred three times more rapidly compared with the formation of the homodimers. As both monomeric forms revealed similar renaturation kinetics, it can be concluded that the first-order rate-determining folding step does not occur during monomer folding but must be attributed to conformational rearrangements of the dimerized, not yet disulfide-bonded protein. These structural rearrangements allow a more rapid formation of intermolecular disulfide bonds between the two different monomers of a heterodimer compared with the formation of the disulfide bonds between two identical monomers. The preferential formation of disulfide-bonded heterodimers from an equimolar mixture of unfolded A- and B-chains is thus a kinetically controlled process. Moreover, similar activation enthalpies for the formation of all different isoforms suggest that faster heterodimerization is controlled by entropic factors.     

Translational control in oocyte development

Translational control of specific mRNAs is a widespread mechanism of gene regulation, and it is especially important in pattern formation in the oocytes of organisms in which the embryonic axes are established maternally. Drosophila and Xenopus have been especially valuable in elucidating the relevant molecular mechanisms. Here, we comprehensively review what is known about translational control in these two systems, focusing on examples that illustrate key concepts that have emerged. We focus on protein-mediated translational control, rather than regulation mediated by small RNAs, as the former appears to be predominant in controlling these developmental events. Mechanisms that modulate the ability of the specific mRNAs to be recruited to the ribosome, that regulate polyadenylation of specific mRNAs, or that control the association of particular mRNAs into translationally inert ribonucleoprotein complexes will all be discussed.