The wild-type allele of tonB in Escherichia coli is dominant over the tonB1 allele,encoding TonBQ160K,which suppresses the btuB451 mutation

The entire coding sequence of the tonB gene, except for nine codons at the 3′ end, was deleted from the chromosome of Escherichia coli. Introduction of the btuB451 suppressor mutant tonB1 into the chromosome of such a tonB deletion strain showed that the tonB1 allele was active as a suppressor in a single copy at 37° C and 42° C but not at 28° C. No temperature dependence was seen when FepA- or FhuA-dependent activities of the tonB1 gene product (TonB_Q160K) were tested. The btuB451 suppressor activity of tonB1 was inhibited by the simultaneous presence within the cells of the tonB ⁺ allele on a multicopy plasmid. This represents the first case of dominance among different tonB alleles. Inhibition of suppression was abolished by overexpression of the btuB451-encoded receptor protein. Competition for binding of TonB⁺ and TonB_Q150K to ExbB was excluded as the cause of dominance. Based on our data we conclude that competition for binding of TonB ⁺ and TonB_Q160K to the btuB451 gene product is the reason for the observed dominance. The implications of these findings for the mechanism of btuB451 suppression by tonB1 are discussed.     

Cytological and Physiological Reasons for the Latent Type of Infection in Sunflower Caused by Plasmopara halstedii

Lightmicroscopy was used to investigate cytological and physiological reasons for the latent type of infection of sunflowers with Plasmopara halstedii. Sections of the hypocotyl of inoculated, but healthy looking plants of compatible and incompatible host-pathotype combinations revealed vital hyphae and oospores, thus indicating an uninterrupted life cycle of the pathogen. Plants with latent infections showed enhanced cell division activities which restricted the pathogen to the cortical parenchyma. Additionally, hypersensitive reactions inhibited further growth in the pith parenchyma. In contrast, for systemic infection a successful invasion by the pathogen of the pith parenchyma of the hypocotyl and a growth of the hyphae faster than the hypersensitive reactions of the host tissue are needed.     

Principes de la lecture critique de la littérature médicale: Illustration urologique

There has been an enormous expansion in scientific literature, especially in the area of health and medicine. At the same time the complexity of the research has increased. Through the reading of medical literature of his field of interest, the physician is in search of useful information. However, reading medical papers is very time consuming and most physicians, for their usual literature review, content themselves with the titles and the abstracts. Moreover, quality and relevancy of the publications vary greatly and the reader must be able to “separate the wheat from the chaff”. Thus the reading of literature needs selection and evaluation. As a result, physicians require critical appraisal skills. The principle of appraisal of medical literature is to assess the value of publications which will influence the medical practice of the reader. The reader has a double objective: to assess the credibility of the publications, and to define the applicability of the publication information. By following eight steps the reader is able to quickly rule out from his reading what is not valid and have an objective look at the quality of the results which are proposed to him. These eight steps comprise the assessment of the study objectives, the study design, the study factor(s), the outcome factor(s), the study population and sample, the confounding factor(s) and bias, the results with their statistical and clinical significance and the power of the study, and, lastly, the synthesis of the reader's judgment. The last word belongs to the clinician facing his patient.     

Acoustic signalling in palaeotropical bushcrickets (Orthoptera: Tettigonioidea: Pseudophyllidae): does predation pressure by eavesdropping enemies differ in the Palaeo- and Neotropics?

When producing its calling song, a male bushcricket exposes itself to predators which use this sound for localization. Male signalling therefore has to be a compromise between attracting females and avoiding predators. In this study, the calling song structure of six Malaysian bushcricket species of the family Pseudophyllidae was examined. The lowest frequency of longdistance signals in insects yet discovered is the 600 Hz produced by Tympanophyllum arcufolium. The peak frequency of all six species and three additional species, from which only handling sounds were examined, was below 12 kHz. The duty cycle (that period of time spent signalling) was low, between one and five percent in four species and more than 20 percent in the remaining two species, typical for species which rely on camouflage. None of the various types of bat avoidance behaviour observed in the neotropical Pseudophyllidae was found in the Malaysian species. This difference is discussed in regard to the possibility of different predation pressures in the Palaeo- and Neotropics.     

Plasma membranes from cardiac cells in culture. Enzymatic radio-iodination,evaluation of preparation and properties of the sarcolemma

Plasma membranes from heart (sarcolemma) were prepared by the method of Kidwai, A.M. ((1975) Methods in Enzymology (Fleischer, S. and Packer, L., eds.), Vol. XXXIA, pp. 134–144, Academic Press, New York). On many occasions the sarcolemmal fraction identified by the enzyme markers such as $\text{(}\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$ banded at heavier densities ($\text{3 > 1.25}\text{g/ml}$) than expected for plasma membrane ($\text{d < 1.15}\text{g/ml}$). Radio-iodination of the membrane was added as an independent marker and conditions for the reproducible preparation of the sarcolemma were studied. Cultured heart cells were enzymatically iodinated under conditions which did not affect viability and labeled primarily the sarcolemma. The distribution of radioactivity in homogenates of cultured cells on the density gradient corresponded to that of the enzymes' activity. The best sarcolemma preparation was obtained with 0.3 M KCl extraction of heart homogenates in the presence of 0.05 M pyrophosphate, especially if the salt was also present during the fractionation by density gradient centrifugation. Alterations in the density were also observed with erythrocytes and cultured liver cells' plasma membrane. The data suggests a meta-stable state of the plasma membranes due to handling or storage which could cause alterations of some of their physical properties (e.g. density).     

Flavanone synthase from Petroselinum hortense. Molecular weight, subunit composition, size of messenger RNA, and absence of pantetheinyl residue.

Flavanone synthase from irradiated cell suspension cultures of parsley was purified to apparent homogeneity. Molecular weights of about 77 000 for the enzyme and about 42 000 for the subunits were determined respectively by sedimentation-equilibrium measurements and disc-gel electrophoresis in the presence of dodecyl sulfate. A specific antiserum was prepared for the enzyme and was used in an assay for flavanone synthase mRNA activity in partially purified RNA preparations. The apparent molecular size of flavanone synthase mRNA was estimated by sucrose gradient centrifugation and gel electrophoresis under partially denaturing conditions. Values of about 17 S and Mr = 0.62 X 10(6) were obtained. The fractionation patterns suggested that flavanone synthase mRNA was homogeneous in size. All together, the results support the idea that the enzyme is composed of two subunits which are probably identical. Amino acid analysis and a microbial assay were carried out to test the possible occurrence of cysteamine, beta-alanine, and pantothenate in the enzyme. The results were negative, indicating the absence of pantetheine or a similar residue. The possible similarity in mechanism between flavanone synthase and 3-oxoacyl-(acyl carrier protein) synthase is discussed.     

Accelerated Adsorption of Bacteriophage T5 to Escherichia coli F, Resulting from Reversible Tail Fiber-Lipopolysaccharide Binding

A dual specificity for phage T5 adsorption to Escherichia coli cells is shown. The tail fiber-containing phages T5(+) and mutant hd-3 adsorbed rapidly to E. coli F (1.2 x 10(-9) ml min(-1)), whereas the adsorption rate of the tail fiber-less mutants hd-1, hd-2, and hd-4 was low (7 x 10(-11) ml min(-1)). The differences in adsorption rates were due to the particular lipopolysaccharide structure of E. coli F. Phage T4-resistant mutants of E. coli F with an altered lipopolysaccharide structure exhibited similar low adsorption for all phage strains with and without tail fibers. The same held true for E. coli K-12 and B which also differ from E. coli F in their lipopolysaccharide structures. Only the tail fiber-containing phages reversibly bound to isolated lipopolysaccharides of E. coli F. Infection by all phage strains strictly depended on the tonA-coded protein in the outer membrane of E. coli. We assume that the reversible preadsorption by the tail fibers to lipopolysaccharide accelerates infection which occurs via the highly specific irreversible binding of the phage tail to the tonA-coded protein receptor. The difference between rapid and slow adsorption was also revealed by the competition between ferrichrome and T5 for binding to their common tonA-coded receptor in tonB strains of E. coli. Whereas binding of T5(+) to E. coli K-12 and of the tail-fiber-less mutant hd-2 to E. coli F and K-12 was inhibited 50% by about 0.01 muM ferrichrome, adsorption of T5 to E. coli F was inhibited only 40% by even 1,000-fold higher ferrichrome concentrations.     

Current management of hypertension in general practice.

An examination of the notes of 697 patients in a random sample of seven general practices in one part of inner London showed that 164 (24%) of 669 had had a blood-pressure recording in a five-year period. Proportions varied between 4% and 36% in the different practices. The blood pressure was raised (systolic greater than or equal to 160 mm Hg or diastolic greater than or equal to 100 mm Hg or both) in 74 patients (45%) whose blood pressure had been recorded, and another recording had subsequently been made in 45 (61%) of these patients. Fifteen (21%) of those with hypertension had not had a blood-pressure recording during the five years before the study. Tranquillisers or sedatives were the commonest drugs used in the treatment of hypertension. As in a study of the management of hypertension in hospital, opportunities provided by visits to the general practitioner were not commonly used for blood-pressure screening, and the discovery of hypertension often did not lead to further action.     

Remission Maintenance Therapy in Acute Myelogenous Leukemia

Because no conclusive evidence as to the efficacy of maintenance chemotherapy in acute myelogenous leukemia (AML) existed, a study to obtain such information was done. Twenty-six adult patients with AML in whom complete remission had been achieved following induction chemotherapy were randomly assigned to receive either maintenance chemotherapy consisting of cytarabine and 6-thioguanine for two days each month or to receive no maintenance therapy. The data showed a significant difference in remission duration between the two groups, with median remission lengths for the maintained and unmaintained groups being 10.3 and 6.7 months, respectively (p<.05). In 46 percent of the maintained patients there were remissions lasting longer than 11 months, whereas in none of the unmaintained patients was there such a prolonged remission. No significant drug-induced toxicity was observed. That the prolonged exposure to these chemotherapeutic agents, which were also used in our induction program, did not adversely affect the rate of successful reinduction therapy was shown by identical 50 percent complete remission rates for second inductions in both groups. In patients with palpable splenomegaly at the time of diagnosis, there was no prolongation of remission with maintenance therapy. These data indicate the potential utility of maintenance chemotherapy for prolonging remission duration in acute myelogenous leukemia.     

Polyacrylamide gel as a medium for DNA dissociation and reassociation

Several properties of thermal denaturation and renaturation of DNA in polyacrylamide gels were investigated: (1) Following electrophoresis the DNA band was scanned and shown to increase in absorbance with increasing temperature. The increase was proportioned to DNA concentration across the peak. (2) The dependence of theT _m on salt concentration over a hundred fold range was similar to that found for DNA in free solution. (3) Denaturation of several DNA samples ranging in G+C content from 26 to 71% was compared in gels and free solution. The relationship betweenT _m and % G+C was virtually identical for both sets of DNAs. (4) The kinetics of DNA renaturation in the gel was followed. Reassociation of bacteriophageT ₄ DNA was 2nd order and proceeded more rapidly in polyacrylamide gels than in free solution.