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M Boublik

Publications and source records attributed to M Boublik.

At least 55 records · Page 3Linked to original sources
PubMed1979

Structure of functional A salina -- E coli hybrid ribosome by electron microscopy.

Small 40S Artemia salina and large 50S Escherichia coli ribosomal subunits can be assembled into 73S hybrid monosomes active in model assays for protein synthesis. The reciprocal combination -- small 30S E coli and large 60S A salina -- fails to form hybrids. The 73S hybrid particles strongly resemble homologous 70S E coli and 80S A salina monosomes. The morphologic differences between the corresponding eukaryotic and prokaryotic ribosomal particles, established by electron microscopy, do not significantly affect the assembly and mutual orientation of 40S A slina and 50S E coli subunits in the heterologous monosome. The fact that the structure of the interface, the supposed site of protein synthesis, is preserved in the active hybrid implies that retention or loss of biologic activity of hybrid ribosomes is determined by the extent of conformational changes in the interface.

Animals↗
PubMed1979

Localization of the decoding region on the 30S Escherichia coli ribosomal subunit by affinity immunoelectron microscopy.

The decoding region of the Escherichia coli ribosome has been localized by affinity immunoelectron microscopy. Valyl-tRNA1Val, derivatized at the alpha-amino end with the dinitrophenyl group, was bound to the ribosomal P site of 70S ribosomes and crosslinked specifically to 16S RNA by 310- to 325-nm irradiation. Previous work has shown that crosslink occurs between the 5' anticodon base of the tRNA and a pyrimidine in the 3' one-third of the 16S RNA. By reaction of the dinitrophenyl group with antibody, dimers of the 30S tRNA covalent complexes were prepared containing one covalently attached tRNA per 30S subunit. Electron microscopic visualization of the antibody attached to the dinitrophenyl group located the position of the 3' end of the tRNA. Several sites, with a strong preference for the large protrusion or cleft region in the upper one-third of the subunit, were found. The multiplicity of sites is likely due to the freedom of orientation of the 3' end of the tRNA which is approximately 80 A from the site of crosslinking. By extrapolating this distance from each of the antigenic sites, we concluded that the anticodon of tRNA when in the P site is probably located in the cleft region of the 30S subunit.

Dinitrophenols↗
PubMed1979

Nucleic acid binding and unfolding properties of ribosomal protein S1 and the derivatives S1-F1 and m1-S1.

The nucleic acid binding and unwinding properties of wild-type Escherichia coli ribosomal protein S1 have been compared to those of a mutant form and a large trypsin-resistant fragment, both reported recently [J. Mol. Biol. 127, 41-45 (1979) and J. Biol. Chem. 254, 4309-4312 (1979). The mutant (m1-S1) contains 77% and the fragment (S1-F1) 66% of the polypeptide chain length (approximately 600 amino acid residues) of protein S1. The mutant is active in protein synthesis in vitro; the fragment, although retaining one or more of the functional domains of S1, is inactive in protein synthesis. We find that m1-S1 is is almost as effective as S1 in binding to poly(rU), phage MS2 RNA and simian virus 40 (SV40) DNA, and in unfolding poly(rU) and the helical structures present in MS2 RNA and phi X174 viral DNA. S1-F1, however, binds to poly(rU) and denatured SV40 DNA, but not to MS2 RNA. It unfolds neither poly(rU), nor the residual secondary structure of MS2 RNA or phi X174 viral DNA. Thus, there appears to be a correlation between the loss in ability of S1 to unwind RNA and the loss in its ability to function in protein synthesis.

Bacterial Proteins↗
PubMed1978

Conformation of dinucleoside monophosphates modified with benzo[a]pyrene-7,8-dihydrodiol 9,10-oxide as measured by circular dichroism.

The conformational properties of GpU modified with the reactive derivative of benzo[a]pyrene, (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, has been investigated utilizing circular dichroism spectroscopy. Binding of this carcinogen to the N2 of G residues in GpU resulted in the formation of four compounds (I to IV) representing two pairs of diastereoisomers. The molar ellipticity values of the modified dimers were approximately twofold higher than those of the modified guanosine monomers. These values were decreased appreciably when the spectra of the dimers were obtained at 80 degrees C or in methanol rather than at 25 degrees C in water, suggesting that under the latter conditions there is a stacking interaction between the carcinogen and the neighboring uridine residue. Based on these results, a conformation is proposed for modified GpU. It includes insertion of the benzo[a]pyrene moiety, by rotation of the modified guanine residue about its glycoside bond, coplanar to the neighboring uridine and perpendicular to the phosphodiester backbone.

Benzopyrenes↗
PubMed1978

Structure of LiCl core particles of 50 S ribosomal subunits from Escherichia coli by electron microscopy.

The structure of 50 S E. coli ribosomal subunits was studied by electron microscopy as these particles were gradually depleted of proteins by incubation with 0.5 to 6.0 m LiCl. Changes observed in the structure of the depleted subunits were correlated with the location of the deleted ribosomal proteins on the control 50 S particle. These changes were particularly striking in the "crown" region, the site of a considerable number of the proteins necessary for the biological activity of the 50 S subunit. Protein L 16, the first to be removed by the LiCl treatment, was found to be essential for the structural integrity of the large subunit through interactions with ribosomal proteins residing in the left-hand side crest and the interface. Based on electron microscopic evidence, a scheme was proposed for the structural changes accompanying the stepwise unfolding of the 50 S E. coli subunit by LiCl.

Bacterial Proteins↗
PubMed1977

Structural subunits of poliovirus particles by electron microscopy.

Electron microscopy of poliovirus particles and empty capsids under various conditions of specimen deposition and staining visualizes the dissociation products of these particles. The dissociation proceeds in steps; it begins with the expansion of particles and leads to the final product of the dissociation--a cluster of several sub-particles of equal size (approx. 100 A in diam.). A scheme of the dissociation is proposed on the basis of the observed intermediates.

Capsid↗
PubMed1976

Demonstration of a core in poliovirus particles by electron microscopy.

Electron microscopic examination of poliovirus in CsCl-solutions without conventional staining with phosphotungstic acid or uranyl acetate revealed the existence of cores inside poliovirus particles. Empty capsids could not be visualized by this technique. Evidently, CsCl can enhance the contrast of the virus particle to an extent sufficient for the study of poliovirus particles by electron microscopy under conditions in which they exhibit specific properties.

Capsid↗
PubMed1975

Polyanion-induced release of polyribosomes from HeLa cell nuclei.

Intact detergent-washed HeLa nuclei contain a population of polyribisomes that were released by exposure to polyanions such as RNA or poly(U). The released material appeared by electron microscopic examination to be particles averaging about 200 to 300 angstroms in diameter. Sedimentation velocity analysis of the released particles indicated that the particles had S20,w values of 75 and 110. The particles stimulated amino acid incorporation in an ascites S-30 or S-100 extract at 2.5 mM Mg2+. Studies with a variety of antibiotics indicated that these polyribosomes were capable of elongating but not initiating protein synthesis. Although these polyribosomes may be of cytoplasmic origin, they appear unique in that agents thought to disperse chromatin are required for their release from the nucleus.

Aminoacylation↗
PubMed1975

Conformations and interactions of histone H2A (F2A2, ALK).

Conformational changes in histone H2A (ALK, F2A2, IIbl) as a function of ionic strength and pH have been followed using high resolution nuclear magnetic resonance (NMR), circular dichroism (CD), and infrared (ir). While change in pH from 3 to 7 (no added salt) causes little structural change, added salt induces the formation of both alpha helix (28 percent maximum) and intermolecular associates in the region of the molecule between 25 and 113. No beta structure was observed at high salt. By the use of different salts it was shown that the structural changes were due largely to nonspecific counterion screening by the added anion. Comparison of observed with simulated NMR spectra has led to the proposal that an ionic strength dependent equilibrium exists between largely unstructured coil molecules and fully structured and aggregated molecules. NMR spectra of H2A obtained in the presence of DNA showed that both the N- and C-terminal regions bind to DNA, i.e., not the portion of the chain that is involved in interhistone interactions.

Amino Acids↗
PubMed1975

Studies on the role and mode of operation of the very-lysine-rich histone H1 (F1) in eukaryote chromatin. The conformation of histone H1.

Proton magnetic resonance, circular dichroism and other studies of whole and cleaved calf thymus histone H1 (formerly F1) reveal the presence of specific folded structures in the region approximately from residue 40--115. Ionic, hydrogen-bond and hydrophobic interactions all appear to contribute to the stability of the structure, which is predicted to contain alpha-helices in regions 42--55 and 58--75. No evidence was found for beta-structures, either inter or intramolecular, or for any structure formation outside the region 40--115. At 18 degrees C and a protein concentration of 2 mM the first-order exchange rate between random-coil and structured forms is slower than 80 s-1; at 40 degrees C the exchange rate is faster than 330 s-1.

Animals↗
PubMed1975

Immunopharmacological studies using 5-hydroxytryptamine antibody.

An antibody to serotonin (5-HT) was tested on several preparations in which 5-HT is considered to be involved. The antibody was capable of effectively competing with 5-HT receptor sites for free molecules of 5-HT. It inhibited the uptake of 3H-5HT by blood platelets and may explain the reduced endogenous 5-HT concentration in blood platelets of immunized rabbits. The decreased platelet content of 5-HT was substantiated by electron microscopic studies which showed a reduction in the number of 5-HT-containing subcellular storage organelles in platelets from these animals. The 5-HT antibody inhibited the 5-HT-induced contraction of aortic strips in a tissue bath preparation. When given intraventricularly, it inhibited for a time the sedative actions of reserpine thus adding new evidence to the often postulated role of 5-HT in the actions of reserpine.

Adenylyl Cyclases↗