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Biomedical subjects

E Kellenberger

Publications and source records attributed to E Kellenberger.

At least 73 records · Page 4Linked to original sources
PubMed1982

The wrapping phenomenon in air-dried and negatively stained preparations.

We demonstrate that the interface energies involved in the direct preparation of supramolecular structures onto supporting films leads very frequently to a smooth wrapping of the supporting film around approximately one third to one half of the structure. We conclude that in such cases the structure is more rigid than the supporting film; examples being ribosomes, small viruses and small glass fragments. Other structures are less rigid and become significantly flattened. Complete flattening is frequently observed with empty virus capsids. The sandwich technique, by which a specimen is placed between two supporting films, in general leads to increased flattening. Only in few cases (e.g. ribosomes) are biological particles rigid enough to resist flattening and become wrapped from both sides.

Coliphages↗
PubMed1982

Involvement of the bacterial groM gene product in bacteriophage T7 reproduction. I. Arrest at the level of DNA packaging.

The multiplication of bacteriophage T7 is blocked in Escherichia coli M. The genetic determinant of this ability (groM) to inhibit T7 growth was transferred to an E. coli K-12 recipient by means of conjugation. We determined at which precise step T7 maturation is blocked. Phage-directed protein and DNA synthesis as well as degradation of host DNA were not qualitatively affected. Instead of infective phages, only preheads were produced. These, however, were maturable in vitro. The newly synthesized phage DNA accumulated in a concatemeric form and matured from its tetrameric or longer forms (very fast sedimenting DNA) only into its dimeric form (fast-sedimenting DNA) or longer forms. The following step, i.e., the maturation of the dimeric to unit-length DNA, was not observed. Since the concatemeric form of T7 DNA accumulated in spite of the presence of maturable preheads, it is likely that the maturation process was blocked at the level of DNA packaging. As intermediates in the packaging process, we found some prehead-DNA complexes. We interpreted these as true assembly intermediates (or breakdown products thereof), since the attached DNA was still in its concatemeric form. This shows that the very first DNA packaging step, the binding of the progeny DNA to the preheads, was obviously not blocked. Rather, a later step, such as the filling of the preheads with T7 DNA or the stabilization of completely packaged particles (i.e., the final cutting of the concatemers into unit-size length), was inhibited.

Bacterial Proteins↗
PubMed1982

Perspectives for achieving improved information by the observation of thin sections in the electron microscope.

Obtaining biologically significant fine detailed information from sections is limited firstly by the unknown distribution of heavy metal stain and secondly by conformational changes induced by dehydration. Only afterwards we have to be concerned with beam induced alterations. By Z-imaging in a STEM, completely unstained material can now become imaged sharply with high contrast. By this the first limitation is eliminated and the second can become explored. For this purpose new resins designed for low temperature embedding might become important. First biological results are presented which illustrate the potential of these techniques: The transmembrane protein of the separate junction has been revealed as such and shown that only the hydrophilic part of the protein is stained by uranyl acetate. This type of staining therefore does not allow the detection of any transmembrane proteins in sections.

Animals↗
PubMed1981

High magnesium content of Escherichia coli B.

We have found that the intracellular concentration of magnesium in exponentially growing Escherichia coli B is much higher than has been previously assumed; it is about 100 mM. Results of equilibrium dialysis suggest that nearly all of this Mg is bound, probably most of it to nucleic acids. These findings could have important consequences for the study of protein-DNA interactions and the in vitro simulation of protein biosynthesis.

DNA, Bacterial↗
PubMed1981

In vitro studies of the fixation of DNA, nucleoprotamine, nucleohistone and proteins.

In view of improving fixation and embedding for thin sections of nuclear material we investigated the crosslinking of selected proteins, nucleic acid and nucleoproteins by observing the eventual gelation of solutions of these substances, which might be produced by current cytological fixatives. For those combinations where gelation occurs, we give thresholds of minimum concentrations required. We discuss the consequences of these findings for the preservation of thin sectioned nuclear structures within cells.

Chromatin↗
PubMed1979

Gene 24-controlled osmotic shock resistance in bacteriophage T4: probable multiple gene functions.

By use of mixed infections with conditional lethal mutations in the head genes and an osmotic shock-resistant mutant we have demonstrated that osmotic shock resistance is controlled by gene 24. Using acrylamide gel electrophoresis combined with the "immune replicate" technique, we confirmed the positions of gene products 24 and 24* (P24 and P24*). In this paper we have still used the notation "P24," etc., for designating the product of gene 23, etc., although we prefer and use in general the designation "gp23" as introduced by Casjens and King (Annu. Rev. Biochem. 44:585, 1975). The reason for using the old notation is because the illustrations were prepared several years ago.) P24 ts showed a significantly slower mobility. Both osmotic shock-resistant and -sensitive mature phages contain 24*. Giants constructed with the Osr phage showed the same surface lattice as normal phage. Through temperature-shift experiments with 24(tsL90) alone and in combinations, we studied the phages which are matured after the shift to permissive temperature in the absence of new protein synthesis. Our results strongly suggest that only a fraction of the total phage complement of gene 24-controlled proteins is involved in determining the phenotype of shock resistance, and the remainder is necessary to mature the head.

Coliphages↗
PubMed1978

Head maturation pathway of bacteriophages T4 and T2. III. Isolation and characterization of particles produced by mutants in gene 17.

We have isolated and characterized two types of particles produced in comparable amounts by mutants in gene 17: the empty large particle and the empty small particle. Dimensions, morphology, stability, and protein composition of the empty large particle are very similar to those of the capsids or empty heads of mature phage. The other type of particle (empty small particle) is very similar in dimensions and stability to the prehead, but differs in that it is composed of processed proteins (gp23, gp24, IpIII). Structural analysis has shown that the protein subunits of the empty small particles are arranged in an unexpanded type of lattice (11.2 to 11.3 nm), whereas the empty large particles have an expanded lattice (13 nm). The characterization of the empty small particle as being composed of cleaved proteins, but still unexpanded, shows that the expansion of the T4 head shell is not necessarily linked to the cleavage of the structural proteins.

Capsid↗
PubMed1977

Studies related to the head-maturation pathway of bacteriophages T4 and T2:I. morphology and kinetics of intracellular particles produced by mutants in the maturation genes.

Mutants in the genes governing the maturation of the head of bacteriophage T4 and in gene 24 were studied by electron microscopy of thin sections. We define morphologically: black particles, comprising mature, stable heads and immature, fragile heads, which break down upon lysis; grizzled particles, which apparently are partially filled or partially emptied; empty large particles without DNA or core which are all the same size as normal heads; empty small particles without DNA and without core which are of the size of the tau particle, which is the prehead of phage T4. The study of single and double mutants of the maturation genes demonstrates that the phenotypes are only different by the proportions of the different particles made except for 17- where only empty small and empty large particles accumulate. The mutants in gene 24 are epistatic on all other mutants. Mutants in gene 17 are epistatic on the remaining ones. The results are consistent with the hypothesis that the products of several of the maturation genes act on DNA to render it competent for packaging while the others act directly on the particle. By this uncoupling, bypasses and abortive pathways can result.

Coliphages↗
PubMed1977

Studies related to the head-maturation pathway of bacteriophages T4 And T2:II. nuclear disruption, protein synthesis and particle formation with the mutant 43-.30-.46-.

We describe the aberrant phage multiplication of the triple conditional lethal mutant 43-(polymerase).30-(ligase).46-(exonuclease) of bacteriophage T4D in which phage DNA replication is arrested but some late protein synthesis occurs (33). The nuclear disruption is indistinguishable from wild type. Forty-five empty small and empty large particles are assembled per cell when the multiplicity of infection (m.o.i.) is 100. This number corresponds closely to the 38 phage equivalents of cleaved major head protein determined biochemically. By reducing the m.o.i. the number of observable particles decreases, reaching 1-5 per cell at an m.o.i. of 5(+5). The total synthesis of phage related proteins is not significantly dependant on the m.o.i. The synthesis of late proteins is about 10% of that of wild type at high m.o.i. and decreases with the m.o.i. The different early and late proteins do not show the same relative proportions as in wild type and respond differently to an increased m.o.i. These and other results are discussed with respect to the role of phage DNA in prehead assembly and head maturation.

Coliphages↗