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Biomedical subjects

M Zama

Publications and source records attributed to M Zama.

At least 37 records · Page 2Linked to original sources
PubMed1982

Micro-environment of the H3-H3 contact region of a nucleosome core particle, as revealed by a lifetime measurement of a fluorescent probe.

A sample of fluorescently-labeled nucleosome core particles was prepared by combining N-(3-pyrene)-maleimide to each of the two cysteine residues of the two H3 histones in the chicken erythrocyte nucleosome core particle, by a method previously reported by Zama et al. (Nucl. Acids Res. 5, 3881 (1978)). The fluorescence spectra and fluorescence lifetime of the sample in solvents with various Na+ concentrations have been examined. Three different types of micro-environment of the fluorescent probe have been found: (i) emits a pyrene dimer fluorescence at 460 nm, (ii) emits a pyrene monomer fluorescence with a long (75-65 ns) lifetime, and (iii) emits a pyrene monomer fluorescence with a short (5-15 ns) lifetime. The manner of dislocation of the two H3 subunits from each other in each of the solutions with different salt concentrations was discussed.

Animals↗
PubMed1982

Small angle neutron scattering studies of the structure of nucleosome cores at low ionic strength.

Nucleosome core particles from chicken erythrocytes have been studied by small angle neutron scattering over the range from 10 to 0.04 mM Na+ at 65 and 100% D2O, and the radii of gyration of the particle were determined. A single transition in the radius of gyration was observed at either D2O concentration. With decreasing the ionic strength from 10 mM, the radius of gyration of the histones obtained at 65% D2O increased from 35 to 40A at about 1 mM ionic strength, whereas at 100% D2O the radius of gyration decreased from 39 to 36A also near 1 mM ionic strength. No loss of the secondary structure of the histones was observed by circular dichroism over the range of the ionic strength examined. These results suggest that at low ionic strength (less than or equal to 1 mM) the histones may locate outside of the nucleosome core particle accompanied by an alteration of the tertiary and/or the quaternary structure of the histone octamer.

Animals↗
PubMed1980

Selective release of HMG nonhistone proteins during DNase digestion of Tetrahymena chromatin at different stages of the cell cycle.

The possible role of LG-1, a Tetrahymena specific HMG protein found in the macronuclear chromatin (Hamana, K. and Iwai, K. (1979) J. Biochem. 86, 789-794), was examined in relation to the chromatin structure. The chromatin isolated from cells synchronized at different stages of the cell cycle contained about one molecule of LG-1 per nucleosome. Limited digestion of the chromatin with DNase I or micrococcal nuclease selectively released LG-1 with the nucleosomal core histones and H1 remained insoluble, bound to the resistant DNA. Depending on the cell stages several types of chromatin structure were distinguished by their nuclease sensitivity. However, the chromatin at different stages exhibited the similar behavior of the LG-1 release with the nucleases as a function of the degree of chromatin solubilization. The results suggest that LG-1 proteins play a role in the chromatin organization which is rather independent of the cell stages.

Animals↗
PubMed1978

Nucleosome conformation: pH and organic solvent effects.

Monomer nucleosomes (nu 1) from chicken erythrocyte nuclei were examined in aqueous buffers (8 greater than pH greater than 3) and in solvent mixtures (i.e., water and ethanol, ethylene glycol, dioxane, dimethyl sulfoxide, 2-methyl-2,4-pentanediol, polyethylene glycol, sucrose, or urea). Circular dichroism, laser Raman spectroscopy of nu 1, and the fluorescence of nu 1 labeled with N-(3-pyrene) maleimide on thiol groups of H3 histone were employed to detect conformational transitions in nu 1. The results of pH studies were as follows: 5.5 greater than pH greater than 4.8, suppression of DNA ellipticity and no change of histone alpha-helix; 4.6 greater than pH greater than 4.2 an irreversible increase in the B character of DNA, a slight loss of histone alpha-helix, and a parallel loss of pyrene excimer fluorescence; 4 greater than pH, aggregation of nu 1 and protonation of the DNA bases C and A. Results obtained in the studies of nu 1 in solvent mixtures included the following: sharp conformational transitions that variously involved an increase in the B character of DNA, a slight loss of histone alpha-helix, and a loss of pyrene excimer. Different solvents required different concentrations to effect these conformational changes.

Alcohols↗
PubMed1976

Structure of wye (Yt base) and wyosine (Yt) from Torulopsis utilis phenylalanine transfer ribonucleic acid.

A fluorescent base wye (Yt base) was isolated from Torulopsis utilis tRNAPhe. The structure was established as 4,9-dihydro-4,6-dimethyl-9-oxo-1H-imidazo[1,2-alpha]purine based on ultraviolet (uv), nuclear magnetic resonance (NMR), and mass spectra, and by direct comparison with synthetic material. The nucleoside, wyosine (Yt), was isolated from purified tRNAPhe by enzymatic degradations followed by column and thin-layer chromatographies. The structure of wyosine is proposed as 3-ribofuranosyl-4,9-dihydro-4,6-dimethyl-9-oxo-1H-imidazol[1,2-alpha]purine (the ribosyl group is attached to the N-9 position of guanine nucleus) on the basis of comparison with model compounds.

Candida↗
PubMed1975

Different effects of polylysine and polyarginine on the transition to a condensed state of DNA in polyethyleneglycol/salt solution.

Circular dichroism spectroscopy has been used to investigate the influence of polylysine and polyarginine on the transition to a condensed state of DNA brought about by high concentrations of polyethyleneglycol and salt. From the dependence on DNA concentration of the CD signals, the anomalous CD of free DNA in polyethyleneglycol/salt solution was attributed to the intermolecular association of DNA molecules. The CD spectral changes in polyethyleneglycol/salt solution of the DNA - polylysine complex were indistinguishable from those of free DNA while the DNA-polyarginine complex suffered much smaller spectral changes as compared with free DNA, at low DNA concentrations where time-independent CD spectra were observed in polyethyleneglycol/salt solution for both the complexed and free DNA. The repression of the spectral change by the latter complex was more remarkable at higher ratios of polyarginine to DNA. The facts indicate that, whereas polylysine binding has little influence on the intermolecular structural transition of double-stranded DNA into a compact molecular configuration in polyethyleneglycol/salt solution, polyarginine binding has an effect of inhibiting the transition.

Animals↗