Cell-free Studies on the Regulation of the Arabinose Operon

A DNA directed, cell-free system which synthesized L-ribulokinase coded by the L-arabinose operon ara OIBAD, has been developed. L-arabinose but not the araC gene product is required for the expression of this operon and, in addition, cyclic AMP and guanosine tetraphosphate are needed for optimal synthesis.     

Cooperation between Carrier-reactive and Hapten-sensitive Cells <Emphasis Type="Italic">in vitro</Emphasis>

THE mechanism, known as the carrier effect, whereby immunity to one or more determinant groups enhances the response to other determinants on the same multivalent antigen, was first recognized in delayed hypersensitivity to haptens, in which, for an appreciable response, the hapten must be coupled to the same protein carrier for priming and challenge^{1, 2}. Carrier specificity has also been demonstrated in the secondary antibody responses to hapten protein conjugates³. Two alternative hypotheses have been advanced to explain this specificity. The “local environment” hypothesis supposes that the hapten-sensitive cell recognizes both the hapten and the carrier determinants. However, the antihapten antibodies produced do not distinguish details of the carrier molecule and so do not reflect the specificity of the cellular receptor. Furthermore, inert spacer molecules inserted between hapten and carrier do not interfere with carrier specificity in the antibody response³. Reflecting current views on the cooperation between thymus-derived (T) and bone marrow derived (B) lymphocytes in the antibody response to various antigens⁴, the second hypothesis invokes two or more cells, one with receptors directed towards the hapten (hapten-sensitive cell), the others specific for the carrier molecule proper (carrier-reactive cells). Supporting this is the observation that pre-immunization to a particular protein carrier alone could potentiate the primary or secondary antihapten response to a hapten conjugated to that protein⁵. In an adoptive transfer system, moreover, the efficiency of antihapten antibody production by cells primed to a particular hapten-protein conjugate and stimulated with the hapten conjugated on a heterologous protein, is significantly enhanced by the introduction of cells primed to the heterologous carrier alone. Anti-carrier serum antibody does not cause such enhancement⁶. The carrier-reactive cells must therefore cooperate in increasing the efficiency of the hapten-sensitive cells in some way other than by providing humoral anti-carrier antibody. Recent work strongly suggests that carrier reactive cells are thymus-derived^{6, 7}.     

Function of the <Emphasis Type="Italic">rel</Emphasis> Gene in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Sokawa et al. suggest that rel^- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited.     

“Pleiotypic Response”

A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells.     

Inhibition of DNA Synthesis but not of Poly-dAT Synthesis by the Arabinose Analogue of Cytidine <Emphasis Type="Italic">in vitro</Emphasis>

Kimball and Wilson¹ reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen² observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators³ had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore⁴ reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler⁵ has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore.     

Endopeptidase Activity of Phage λ-Endolysin

JACOB and Fuerst^1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ³ which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli² and one would therefore expect its substrate to be murein.     

Induced Bivalent Interlocking and the Course of Meiotic Chromosome Synapsis

WHEN chromosomes pair at meiosis the bivalents so formed do not normally interlock. Heat-treatments can, however, induce bivalent interlocking in the locust Locusta migratoria. Only the longest bivalents interlock and usually only two are found per cell; two “rod” bivalents, with single chiasmata, two “ring” bivalents, each with two or three chiasmata, or one “rod” and one “ring” bivalent (Fig. 1a, b and c). The nature of this interlocking and the metaphase orientational and congressional properties of interlocked bivalents are analysed in detail elsewhere¹.     

Basi ultrastrutturali della contrazione miocardica: la distensibilitá passiva del sarcomero quäle espressione della funzione ventricolare

Riassunto Dopo la discussione del metodo per la fissazione in toto del ventricolo sinistro a differenti pressioni passive di riempimento vengono riportati i dati biometrici ultrastrutturali della componente contrattile, dei mitocondri e del sistema trasversale del reticolo delle cellule miocardiche.L'aumento della pressione intraventricolare determina un rapido allungamento del sarcomero che raggiunge il valore di 2,2 a 10 mm Hg mentre il suo incremento è proporzionalmente minore ad elevate pressioni passive.Le miocellule degli strati sottoendocardici allo stesso livello pressorio sono inoltre maggiormente distese rispetto a quelle degli altri strati. Dall'analisi dei grafici relativi alle curve tensione/lunghezza e tensione/volume, risulta, inoltre, che l'allungamento dei sarcomeri è solo parzialmente responsabile dell'aumento della capacità ventricolare, per cui si può supporre che avvenga un nuovo ordinamento spaziale dei vari fasci nel contesto della parete.La distensibilitá passiva del sarcomero, qualora sia rapportata a precisi dati anatomo funzionali della cavità ventricolare, può essere ritenuta un valido modello per lo studio della contrattilità miocardica in condizioni normali e patologiche.

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Ultrastructural bases of myocardial contractility: the passive distensibility of the sarcomere, as an index of ventricular function

Summary Having described a method of total fixation of the left ventricle at different levels of passive pressure, the Authors refer about biometrical and ultrastructural data of the contractile component, the mitochondria and the transversal reticular system of the heart muscle cells.The raise of pressure in the ventricle determines a rapid increase of the sarcomere length, which can reach the value of 2,2 at a pressure of 10 mmHg. However, with higher passive pressures, a proportional minor increase of the sarcomere is found.With the same pressure, the myocells situated directly under the endocardium, became more distended than the myocells situated further in the myocard.From the analysis of the diagrams tension/length and tension/volume follows that the increase of the sarcomere is only partially responsible for the augmentation of the ventricular capacity. It is therefore possible that at the same time a new spatial arrangement of the fibres occurs.The passive distensibility, studied under any functional and anatomical condition of the ventricle, may be considered a valuable in vitro model for the study of the myocardial contractility under physiological as well as pathological conditions.

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La ricerca è stata eseguita con i fondi del C.N. R.