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     

Temperature dependence of the barley root plasma membrane-bound Ca2+- and Mg2+-dependent ATPase

Arrhenius plots of the maximal velocities for the Ca²⁺-and Mg²⁺-dependent ATPase activities found in a plasma membrane-rich microsome fraction isolated from the roots of barley ( Hordeum vulgare L. cv. Conquest) were nonlinear. Arrhenius plot analyses using a relation which produced curvilinear Arrhenius plots accurately fit the data and allowed the calculation of the activation enthalpies and molar heat capacities of activation. The temperature dependence of the computed Km values for the Ca²⁺- and Mg²⁺-dependent ATPase activities was complex, with the highest enzyme-substrate affinities being obtained near the barley seedling growth temperature (16°C). Using electron paramagnetic resonance spectroscopy with amphiphilic cationic and anionic spin probes, it was possible to demonstrate that temperature changes and increasing Ca²⁺ concentrations could alter the mobility of the membrane lipid polar head groups. Inhibition of the ATPase activities by high levels of Ca²⁺ may result from a Ca2+-induced reduction in the lipid polar head group mobility. The possible role of lipid polar head group-protein interactions in the complex temperature dependence of the barley root ATPase kinetic constants is discussed.     

O(3)-(2-Acetylamino-2-deoxy-β-d-glucopyranosyl)-oleanolic acid,a novel triterpenoid glycoside from two Pithecellobium species

A new triterpenoid glycoside containing an amino sugar moiety has been isolated from Pithecellobium cubense and P. arboreum and identified as O(3)- (2-acetylamino-2-deoxy-β-d-glucopyranosyl)oleanolic acid. β-d-Glucopyranosyl-α-spinasterol was also obtained from P. cubense.     

Steroidogenesis in isolated adrenocortical cells. Correlation with receptor-bound adenosine 3′:5′-cyclic monophosphate

Because several groups have recently questioned a mediating role for cyclic AMP in adrenocortical steroidogenesis, we analysed the problem in more detail by measuring three different cyclic AMP pools in cells isolated from decapsulated rat adrenals. Extra-cellular, total intracellular and bound intracellular cyclic AMP were determined by radioimmunoassay in comparison with corticosterone production induced by low corticotropin concentrations. The increase in extracellular and total intracellular cyclic AMP with low corticotropin concentrations was dependent on the presence of a phosphodiesterase inhibitor and short incubation times. Bound intracellular cyclic AMP was less dependent on these two parameters. In unstimulated cells cyclic AMP bound to its receptor represents only a small fraction of the total intracellular cyclic AMP. After stimulation by a concentration of corticotropin around the threshold for corticosterone production, an increase in bound cyclic AMP was observed which correlated very well with steroidogenesis both temporally and with respect to corticotropin concentration. This finding was complemented by measuring a concomitant decrease in free receptor sites. Full occupancy of the receptors was not necessary for maximal steroidogenesis. Binding kinetics of cyclic [(3)H]AMP in concentrations equivalent to the intracellular cyclic AMP concentration suggest the presence of at least three different intracellular cyclic AMP pools. These observations are in agreement with a possible role for cyclic AMP as a mediator of acute steroidogenesis induced by low corticotropin concentrations.     

Activation of old cuticle chitin as a substrate for chitinase in the molt of Manduca

During the molt, chitin in the old cuticle of $\text{Manduca}$ is digested by chitinase taken up from molting fluid, but the chitin in intact (= premolt) cuticle is not accessible to chitinase. As a prerequisite of digestion, old cuticle chitin is rendered competent to serve as chitinase substrate in a reaction attributable to trypsin-like proteolytic activity of molting fluid.     

TECHNICAL CONSIDERATIONS IN CANNULATING THE ASCENDING AORTA

A successfully used technique of aortic arch cannulation is reported. This cannula is inexpensive and can be made easily in the hospital. The position and advantages of the cannula are discussed.     

C2 deficiency in man. genetic relationship to a mixed lymphocyte reaction determinant (7a*)

Three unrelated individuals with, respectively, lupus erythematosus, polyarteritis, and membranoproliferative glomerulonephritis and totally deficient in the second component of complement are demonstrated to be mutually poorly reactive in mixed lymphocyte culture and homozygous for the mixed lymphocyte reaction determinant (MLR-S or LD) short 7a (7a^*). The gene controlling the elaboration of C2 in man is shown to be separate from, and probably to map outside of, the second locus ofHL-A and theMLR-S locus. Genetic linkage disequilibrium is strongly suggested between HL-A 10, W18, 7a^*, and C2 deficiency.