Albrecht K. Kleinschmidt

Denaturation pattern of the DNA of adenovirus type 2 as determined by electron microscopy.

Abstract The DNA of human adenovirus type 2 has been found in electron microscope studies of DNA-protein monolayers to be a linear molecule which is 10.9 μ long. When partially denatured by heating at low salt concentrations and in the presence of formaldehyde to various temperatures in the range between 52 and 58 °C, denaturation sites can be recognized in the electron microscope, and a map of these regions can be constructed. These sites presumably correspond to segments in the DNA molecule which are rich in adenine thymine base pairs. In the range of 10 to 25% denaturation (55 to 57 °C), a unique melting pattern is found in adenovirus type 2 DNA with three major and one minor denaturation sites. On a unit length scale of the molecule, these sites are located between 0 and 0.15, 0.5 and 0.6, and 0.8 and 1.0; and at 0.4. These findings argue strongly against the possibility that the gene sequence in adenovirus type 2 DNA is circularly permuted. Fragments of adenovirus type 2 DNA generated by shear breakage of the molecule can be separated in Hg(II)-Cs 2 SO 4 density gradients. This finding supports the interpretation that adenine-thymine-rich clusters are distributed unequally in adenovirus type 2 DNA.

Acetyl Coenzyme A Carboxylase: Filamentous Nature of the Animal Enzymes

Acetyl coenzyme A carboxylases purified from several animal tissues exist as enzymatically active polymeric filaments of high molecular weight and have simillar electron microscopic, hydrodynamic, and catalytic properties. These filaments reversibly dissociate into inactive protomers of uniform size. Their re-assembly into catalytically active filaments is promoted by the presence of an allosteric activator.

Physical studies on the structure of yeast mitochondrial DNA

Abstract The physical conformation of DNA isolated from the mitochondria of the yeast Saccharamyces cerevisiae has been studied using the techniques of sucrose gradient zone sedimentation and CsCl density-gradient equilibrium centrifugation. The DNA appears mainly as a linear double helix 4.0 to 4.5 μ in length. Some of these molecules possess cohesive termini which interact to produce hydrogen-bonded circles. Linear dimers and trimers of the basic unit length can be seen in electron micrographs. A small percentage of the total mitochondrial DNA molecules are covalent, superhelical circles.

Electron microscopy of RNA strands released from individual reovirus particles

Abstract A gradual release of double-stranded RNA occurred after the spreading of reovirus particles on urea in the cold. Electron microscopy of virus-protein monolayers showed that each virion expelled about 11 fragments of 8.3 μ, maximum total length. This gives an estimated RNA molecular weight between 17 and 22 million daltons per virion. The length distribution of the fragments was trimodal, with peaks at 0.38, 0.66 and 1.13 μ, but there was large variation of filament lengths in each peak.

Structural studies on the capsid of Caulobacter crescentus bacteriophage φCbK

Electron microscopy, combined with optical diffraction, has been used to investigate the topological structure of the head or capsid of Caulobacter crescentus bacteriophage φCbK. Analysis of optical diffraction patterns from micrographs of negatively stained and metal-shadowed phage heads has enabled a model to be constructed for the non-isometric capsid. The model consists of a prolate cylindrical surface lattice with 5-fold rotational symmetry closed at each end by a pentagonal pyramidal cap. Optical filtering and image reconstruction gave additional information on the distribution of protein in the surface of the φCbK capsid. The protein composition of the phage has been determined by gel electro-phoresis, the results indicating that three major proteins make up the capsid. The relation between the numerical distribution of these proteins and the proposed model for the capsid is discussed.

Caulobacter crescentus bacteriophage φCbK: Structure and in vitro self-assembly of the tail

Abstract Electron micrographs of negatively stained and platinum-shadowed bacteriophage φCbK have been analyzed by optical diffraction and computer Fourier transformation. The results show that the phage tail is a helical “stacked disc” structure with an annular repeat of about 38 A and with 3-fold rotational symmetry about the helix axis. Phage tails exhibited lateral and rotational flexibility and were found to possess variable helical parameters. The smaller angle of rotation about the helix axis between equivalent asymmetric units on adjacent discs measured from a number of tail images was found to have an average value of 41.5±0.9 °. Cross-sectional views of short tail fragments were obtained after sonication at 0 °C. These views confirmed the 3-fold symmetry of the 38 A annular unit, which most probably consists of three identical subunits of the major tail protein. Formation of extended tail polymers, both linear and circular, was found to take place spontaneously in vitro after sonication. On the basis of these results, a low-resolution model for the tail helix is presented. The questions of head-tail symmetry mismatch in the phage and of tail length regulation are discussed.

Subunit size and paracrystal structure of avian liver acetyl-CoA carboxylase☆

Abstract The subunit molecular weight of chicken liver acetyl-CoA carboxylase has been redetermined by immunoprecipitation and sodium dodecyl sulfate gel electrophoresis. In the presence of parotid trypsin inhibitor, the immunoprecipitate gave a single band corresponding to a molecular weight of 230,000, which was also found to contain bound biotin. From the biotin content of the protomer (1.0 prosthetic group per 480,000 daltons) it appears that it consists of two non identical subunits, both with molecular weights of approximately 230,000. Electron microscopy has been carried out on the active filamentous form of the enzyme and on paracrystals formed under high-salt conditions. These indicate that the filaments are readily distortable helical ribbons, with an approximate axial repeat of 1100 A, containing eight protomers. The paracrystals are made up of a staggered lateral packing of filaments.

Electron microscopic studies of polyoma DNA released in protein monolayers

Abstract Twisted DNA rings were released from polyoma virus particles upon spreading on a protein film over a denaturing hypophase of urea and sodium perehlorate. Conformational changes were observed while the DNA molecules were irreversibly adsorbed to the monolayer. In our preparations, 80% of the DNA rings first appeared as twisted molecules and 15% as open rings, before all molecules in the monolayer were slowly denatured to tightly coiled forms. 5% were linear forms.