Engineering of lactose metabolism inE. coli by introducing β-galactosidase/galactokinase fusion enzymes

Summary A series of plasmids encoding -galactosidase/galactokinase fusion proteins with connecting linkers of different lengths and properties separating the enzyme moieties were made.E. coli cells harbouring the genes for these bifunctional enzymes were grown on minimal media with lactose as carbon source in order to asses possible metabolic effects. Differences in growth rates were observed when the cells contained a scavenger enzyme, galactose dehydrogenase, competing with galactokinase for the galactose formed by -galactosidase.E. coli cells coding for fusion proteins with long linkers then reflected markedly slower growth rates.     

Nucleotide sequence and phylogenetic implication of the ATPase subunits β and ε encoded in the chloroplast genome of the brown alga Dictyota dichotoma

We have cloned and sequenced the genes atpB and atpE, coding for CF₁ subunits and , respectively, of the chloroplast genome of the brown alga Dictyota dichotoma. Although the coding site of atpE cannot be demonstrated by heterologous Southern hybridizations, a 417 bp reading frame 3 to atpB was identified as the gene atpE by sequence similarities with atpE genes from other sources. A maximum sequence identity of 30% is found between the predicted amino acid sequence of the Dictyota subunit and the corresponding cyanobacterial subunits. Including conserved amino acid replacements, the Dictyota subunit exhibits about 70% sequence similarity with the cyanobacterial and land plant subunits. As in cyanobacteria, the atpE gene does not overlap the preceding gene atpB. The deduced amino acid sequence of atpB is 74–79% identical to the corresponding cyanobacterial and chloroplast subunits. Entirely conserved are regions referred to as the catalytic and/or regulatory sites of ATP formation, including interacting regions between subunits and . A phylogram predicted from F₁/CF₁- subunits of eleven different organisms suggests a common evolutionary origin of plastids from chlorophytes and brown algae.     

Dynamics of the cytoskeleton of epidermal cells in situ and in culture

Summary The cytoskeleton of primary tissue-culture cells from the epidermis of Xenopus laevis tadpoles was investigated by phase-contrast, immunofluorescence, and electron microscopy. The connection between the arrangement of different types of filaments and the mechanical properties of the epidermis is discussed. The bilayered epidermis attains stability from thick bundles of tonofilaments interconnecting the basal desmosomes. Twisting of tonofilaments around each other can explain the occurrence of elastic filamentous curls forming a meshwork braced between rows of small desmosomes in the apical region of the epidermis. Actin is arranged as a diffuse meshwork and sometimes forms bundles intermingling with tonofilament bundles. Surface membranes and rows of small desmosomes are delineated by actin and contain -actinin. Actin raises the tension for rounding and spreading of cells. Microtubules stabilize already well-developed lamellae.     

Volume elasticity of the ocular avascular compartment in vivo and post mortem

By considering the frequency dependence of the ocular volume elasticity it is possible to locate the static volume elasticity function of the avascular compartment of the eye in vivo. The procedure used involved measuring the dynamic volume elasticity function E=f(P, v), where E=volume elasticity, P=intraocular pressure, and v=frequency, in vivo and post mortem at a frequency higher than the apparent upper mechanical response frequency of the intraocular vascular bed. In addition, post mortem measurements were made of the volume elasticity function at a frequency which was as low as experimentally possible. For practical purposes the latter volume elasticity function may serve as an estimate of the static elasticity function of the avascular compartment in vivo. This is possible in all cases because at the high frequency level the dynamic volume elasticity functions measured in vivo and post mortem are identical.Partly presented by the first author at the 4th Mackenzie Symposium, Stirling 1977Decaased 18.3. 1980     

Fine structure of a mandibular stretch receptor in Thrips physapus L. (Thysanoptera,Insecta)

Summary Only one non-ciliary proprioceptor is developed on the mandible of Thrips. It consists of two bipolar, multiterminal sense cells, the dendrites of which form a strand extended between the tentorium and the back mandibular margin. The dendritic terminals are embedded in an electron-dense, homogeneous matrix, which obviously represents the stimulus transmitting structure. The strand is stretched, if the mandible is moved forwards and upwards. In Thrips, the system of proprioceptors monitoring the mandibular movement is reduced extensively compared with other pterygote insects. This is linked up with the far-reaching reduction of the mobility of the mandible itself.This study is dedicated to Mrs. Signe Ulmer, in memory of her winning nature, her invaluable assistance, and her disciplineSupported by a grant from the Deutsche Forschungsgemeinschaft (Ho 826/2-2)     

D-Glucose Transport in Cultured Cells of Neural Origin: The Membrane as Possible Control Point of Glucose Utilization

Abstract: The function of plasma membrane as control point of glucose metabolism has been studied in confluent monolayer of C1300 neuroblastoma (N2A) and glioma (C6) cells. In neuroblastoma, steady state intracellular glucose concentration reached the extracellular levels, while intracellular contents in C6 glioma cells remained very low. In C6 glial cells the amount of glycogen as source of energy was much higher than that found in C1300 neuroblastoma cells. Influx rates of D-glucose in C6 glioma cells were only half those found in neuroblastoma cells. During the influx period (0-40 s) the transport of glucose in these cells did not exceed the phosphorylation rate, whereas a steady, time-dependent increase in glucose content was observed in neuroblastoma cells. While glucose uptake in neuroblastoma cells seems to be regulated at the level of phosphorylating enzymes, the control point in C6 glioma is believed to be membrane transport.     

Unusual behaviour of SPO1 DNA with respect to restriction and modification enzymes recognizing the sequence 5''-G-G-C-C

Summary SPO1 DNA contains only 5 cleavage sites for restriction enzymes which recognize and cleave the sequence 5-G-G-C-C (HaeIII or BsuR). Fragments of SPO1 DNA cloned in E. coli to substitute 5-hydroxymethyluracil (HMU) by thymine (T) remain resistant to HaeIII indicating that this unexpectedly small number of cleavages by HaeIII is not correlated with the presence of HMU in the normal phage DNA. It was previously shown that SPO1 is neither subject to B. subtilis R restriction (Trautner et al., 1974) nor modification in vivo (Günthert et al., 1975). We now show that SPO1 DNA can however be restricted and modified in vitro.