The tetracycline resistance transposons Tn1721 and Tn1771 have three 38-base-pair repeats and generate five-base-pair direct repeats

Summary The 10.7 kilobase (kb) tetracycline resistance transposons Tn1721 and Tn1771, isolated from disparate sources, are completely homologous on the basis of heteroduplex analyses. Both transposable elements are capable of forming multiple duplications of a 5.3 kb portion encompassing the resistance genes (tet region). A model accounting for both, recA-independent translocation and recA-dependent amplification, postulates two direct and one inverted repeat as essential constituents of the transposons. DNA sequence analyses of Tn1721 and Tn1771 have substantiated this model. They demonstrated three identical 38 base pair repeats identically in both transposons dividing them into a minor transposon and a tet region. Identical sequences of at least 87 base pairs providing recombination hot spots for gene duplication have been found at the ends of the repetitious tet region. Translocation of Tn1721 and Tn1771 generates five base pair direct repeats at the respective sites of insertion. On the basis of the heteroduplex molecules and sequences analyzed the two transposons are identical.To Professor Wolfram Heumann on the occasion of his 65th birthday     

Methane formation from fructose by syntrophic associations of Acetobacterium woodii and different strains of methanogens

When Acetobacterium woodii was co-cultured in continuous or in stationary culture with Methanobacterium strain AZ, fructose instead of being converted to 3 mol of acetate was converted to 2 mol of acetate and 1 mol each of carbon dioxide and methane, showing that interspecies hydrogen transfer occurred. In continous culture the organisms formed a close physical association in clumps; the doubling time for each organism was 6h at 33°C. Methane mainly was derived from carbon positions 3 and 4 of the sugar, but other carbons also yielded methane; this was shown to be due to carbon dioxide-acetate exchange reactions by A. woodii in a manner similar to that carried out by Clostridium thermoaceticum. Four other methanogens, Methanobacterium M.o.H. and M.o.H. G, Methanobacterium formicicum, and Methanosarcina barkeri (not acetate-adapted) also produced similar results, when co-cultured with A. woodii.     

Immunological analysis of hemoglobin transition during metamorphosis of normal and isogenicXenopus

Summary Antisera against larval and adultXenopus hemoglobins as well as adult human hemoglobin showed no cross-reaction when tested by immunodiffusion against each heterologous antigen. In this test hemoglobin of a single animal produced two precipitation lines for larvae, but only one for adult stages. Immunoelectrophoresis also revealed more complex precipitation patterns for larval than for adult hemoglobins. Hemoglobin of the isogenic hybrid cloneXenopus laevis/X. gilli also reacted with antisera against normalXenopus hemoglobin.Quantitation of hemoglobins, analyzed by radial immunodiffusion showed fewer than 1% of adult hemoglobin in red cells of larvae, but 30% at completion of metamorphosis. Two weeks later adult hemoglobin attained over 90%, and in red cells of adultXenopus an average of 1% larval hemoglobin were detected.The relatively short transition period suggests that the loss of larval hemoglobin may be due to the elimination of larval red cells, and that the increase in adult hemoglobin may be indicative of a new cell line.     

Analgesic effect of antagonists of substance P

[D-Pro²,D-Phe⁷,D-Trp⁹]-SP and [D-Pro²,D-Trp^7,9]-SP havebeen shown to be antagonists of substance P. The hindlimb scratching syndrome of mice, known to be caused by substance P was absent when these peptides were injected into substance P-treated mice. Substance P shortens “tail withdrawal time” from hot water; the two peptides greatly prolonged tail withdrawal time. Antidromic stimulation of the saphenous nerve (rat), known to release substance P and to induce vasodilatation plasma extravasation, was also greatly inhibited by [D-Pro²,D-Phe⁷,D-Trp⁹]-SP. These peptides presumably cause anti-nociceptor effects (analgesia) by inhibition of substance P at receptors and favor the concept that substance P is a sensory neurotransmitter of nociceptive messages.     

Catabolite repression of different inducible enzymes inEscherichia coli and the effect of cAMP

Simultaneous induction of two enzymes sensitive to catabolite repression does not lead to an additive decrease of the specific activity of the two. Exogenously added cAMP increases the specific activity of catabolically repressed enzymes, irrespective of whether the enzyme is induced separately or simultaneously with another enzyme. In the presence of 12 different substrates metabolized by inducible enzymes glucose does not bring about catabolite repression. Synthesis of cAMP is identical with that occurring under conditions when glucose brings about catabolite repression.     

Mucidin-nonproducing mutants ofOudemansiella mucida

Mutants ofOudemansiella mucida, blocked in the biosynthesis of the antibiotic mucidin, were obtained at a 0.28 % frequency after the application of N-methyl-N’-nitro-N-nitrosoguanidine (MNG) to basidiospores under conditions leading to 0.5–5.0 % survival rates. Loss of antibiotic activity was in most isolates accompanied by a decrease in mycelium growth rate and a suppression of dikaryotizing and fructification ability. Recombination analysis of two stable mutants revealed that the block in mucidin synthesis is the result of mutation in the same chromosomal gene(muc). In contrast to the action of MNG, UV-irradiation leads neither to the loss of biosynthetic activity nor to any morphological change.     

Characterization of dicyclohexylcarbodiimide binding sites in beef-heart mitochondria.

Binding studies with [¹⁴C]-dicyclohexylcarbodiimide showed the presence of binding sites in the beef-heart mitochondrial membrane at a concentration of 1.8 nmol/mg protein (1.4 sites per cytochrome a+a₃). Saturation of these sites correlated with the inhibition of the ATPase activity. The maximum binding capacity could be related with the amount of F₁-ATPase in mitochondria from various tissues.     

The cycling of cadmium and mercury between substrate and fruiting bodies of Agrocybe aegerita (a fungal model system)

Summary The cycling of cadmium and mercury between substrate and fruiting bodies in a model system with wood colonizing basidiomycete Agrocybe aegerita was studied. When radiolabeled ¹⁰⁹CdCl₂ and ²⁰³HgCl₂ were applied to the fruiting bodies of the first flush, they were translocated via substrate into successive harvests. Cadmium and mercury displayed different patterns of distribution in the system. On a percent basis, more cadmium went from the fruiting bodies into the substrate and was retained there. Only minor portions of the metal were translocated into consecutive crops. In contrast, more mercury was retained in the treated fruiting bodies. The fraction which had penetrated into the substrate, however, was more easily translocated into fruiting bodies of successive crops. When calculated on a dry weight basis, the amount of both metals decreased in consecutive harvests.At the end of the experiment, in following distribution patterns for cadmium and mercury were observed: Cd²⁺: first crop (treated), 9.5%; substrate, 77%; combined successive crops (untreated), 9.5%; Hg²⁺: first crop (treated), 36.5%; substrate 21.5%; combined successive crops (untreated), 37%. The patterns reveal that mercury is more mobile in the substrate and therefore more easily translocated to successive fruiting body generations. Hence, from a nutritional point of view, mercury would seem to be more hazardous than cadmium.