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E Delain

Publications and source records attributed to E Delain.

At least 73 records · Page 4Linked to original sources
PubMed1978

Electron microscope fluoro-autoradiography: improvement of efficiency.

The fluorographic process for enhancement of the autoradiographic detection of beta-ray emitted by tritium has been successfully adapted to electron microscope autoradiography. An original scintillator plastic film helped to increase the detection yield of electrons up to 80% without alteration of the morphological aspect of the autoradiograms, and without increasing background fog or causing apparent loss of resolution.

Animals↗
PubMed1977

Electron microscopy analysis of the interaction between Escherichia coli DNA-dependent RNA polymerase and the replicative form of phage fd DNA. 1. Mapping of the binding sites.

The interaction of Escherichia coli DNA-dependent RNA polymerase (EC 2.7.7.6) with the replicative form of the DNA from the filamentous coliphage fd cleaved by the restriction endonuclease HindII has been studied by electron microscopy at low and high ionic strength. In the presence of ATP or GTP, and heparin, RNA polymerase binds to fd replicative-form DNA at a few specific sites which have been mapped. The map was oriented so that transcription is from right to left. Three main GTP initiator sites are found at 15%, 82% and 94% of the genome length. One main ATP initiator site is found which cannot be mapped with the same accuracy, and which is localized between 38% and 50%. In the absence of initiator triphosphates and heparin, the binding of the enzyme to fd DNA is much more heterogeneous and therefore the mapping is more difficult. Nevertheless it seems that the preferential binding regions correspond to the specific sites mapped in the presence of GTP or ATP. The mean number of polymerase molecules bound to DNA as a function of the molecular ratio enzyme to DNA present in the mixture has been determined. From these results a binding isotherm can be obtained. The apparent equilibrium constant (K approximately 10(9) M-1) which is derived certainly represents an under-estimated value, as discussed.

Binding Sites↗
PubMed1977

Electron microscopy analysis of the interaction between Escherichia coli DNA-dependent RNA polymerase and the replicative form of phage fd DNA. 2. Analysis of the dissociation kinetics.

The kinetics of dissociation of the fd DNA - RNA-polymerase complex has been analyzed. Heparin was added to a solution of the enzyme - DNA complex in order to trap free polymerases. At different times after, samples were taken and analyzed by electron microscopy to determine the mean number of enzymes bound per DNA molecule. Unexpectedly, the measured dissociation is not a first-order reaction. The apparent rate constant increases with heparin concentration in the range between 0.001 and 2 mg/ml. These results strongly suggest the existence of a direct transfer process of RNA polymerase to heparin, bypassing the rate-limiting step of dissociation of the enzyme - DNA complex to free enzyme. Theoretical analysis of the direct-transfer model shows that the rate constant of dissociation should level off at high heparin concentrations: measurements of the residual transcription activity show that this is the case. From these experiments, the equilibrium constant of the DNA - RNA-polymerase complex can be determined. The value K = 10(12) M-1 which is obtained solves a striking paradox which existed because measurements performed in other laboratories indicated K = 10(14) M-1, which is greater than the equilibrium constant of the lac-repressor - lac-operator complex (=10(13) M-1).

Coliphages↗
PubMed1977

Ultrastructure of spontaneously differentiated human malignant melanocytes cultured from primary tumors.

Ultrastructural study of early subcultures and established lines of human malignant melanocytes derived from primary tumors showed that melanocytes passed through a phase of dedifferentiation during which they took on a fibroblast-like appearance; then they had a phase of spontaneous redifferentiation. The fibroblast-like cells were characterized by the presence of network-like organelles in their cytoplasm, and the melanocytes by melanosomes.

Cell Differentiation↗
PubMed1976

Gene expression during the differentiation of myogenic cells of the L6 line.

The problem of the mechanistic relationship among the different phenotypic expressions in an established myogenic line was approached by blocking cell fusion at different developmental stages, by addition of cytochalasin B. The addition of the drug to cultures at the time when the first two myotubes appeared on the dish, blocked fusion, but did not affect DNA synthesis, expression of myosin, phosphorylase, phosphocreatine kinase, phosphorylase kinase or glycogen synthetase, nor the organization of the elements of the hexagonal lattice. It is concluded that cell fusion is not a prerequisite for the expression of the differentiated phenotype.

Cell Differentiation↗
PubMed1975

Electron-microscopic mapping of AT-rich regions and of E. coli RNA polymerase-binding sites on the circular kinetoplast DNA of Trypanosoma cruzi.

Partial alkaline denaturation of the circular kinetoplast DNA (kDNA) of Trypanosoma cruzi has shown the existence of 4 small, well-defined AT-rich regions with an average size of about 200 base pairs. They are almost equally distributed, separated by approximately 90 degrees on the circular molecule. All minicircles, whether free or linked in networks, have the same denaturation pattern and, therefore, seem to contain the same information. The long linear molecules present in low amounts in the kDNA samples do not show the same denaturation pattern. Partial denaturation of molecules in larger associations indicates that the circular units may be linked to each other by one strand only. kDNA can be transcribed in vitro by the RNA polymerase of E. coli. RNA polymerase-kDNA complexes have been studied in the electron microscope. By spreading the DNA-protein complexes by adhesion to positively charged carbon films and dark-field observation, it was possible to show the existence of 4 specific binding sites of the E. coli RNA polymerase on the kDNA circles. Comparing the position of the polymerase-binding sites and the AT-rich melted zones, it is suggested that a correlation exists between the two. As had been shown in earlier work, the replication of circular kDNA can be blocked by treating the trypanosomes with the trypanocidal drug Berenil. The comparison of the relative position of the Berenil-blocked replication forks with the position of the 4 denaturation loops shows that the DNA replication is stopped at these AT-rich regions. Since there is evidence that Berenil binds preferentially to AT-rich DNA and seems to be involved in inhibition of DNA replication, the following hypothetical model can be proposed. The replication of the circular kDNA molecules is discontinuous and involves the synthesis of RNA primers; when Berenil is bound to the AT-rich regions, synthesis of new RNA primers is inhibited and replication is blocked at these points, leading to the accumulation of replicating intermediates with defined branch lengths.

Animals↗
PubMed1972

Replicating, convalently closed, circular DNA from kinetoplasts of Trypanosoma cruzi.

When Trypanosoma cruzi are treated with Berenil, a trypanocide, their kinetoplast DNA contains an increased proportion of double-branched circular molecules. These replicating molecules have closed-circular template strands; their decrease in density when complexed by ethidium bromide in a cesium chloride gradient is proportional to the length of the replicated segments. Replication seems to be blocked at specific points, which are equidistantly spaced along the circular kinetoplast DNA molecules. Analysis of about 800 replicating forms showed that the lengths of the replicated branches are not distributed at random, but into several populations, which correspond to multiples of 15% of the total contour length of 0.5 mum. This distribution evokes a discontinuous replication process. The problem of whether kinetoplast DNA is synthesized by successive replication units, or whether and how Berenil might induce specific blocking of DNA replication, is discussed.

Acetates↗