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Biomedical subjects

J Bonner

Publications and source records attributed to J Bonner.

At least 73 records · Page 4Linked to original sources
PubMed1977

Physical properties of chemically acetylated rat liver chromatin.

The physical properties of rat liver chromatin and nucleosomes acetylated with acetic anhydride were examined in order to clarify the mechanism by which chemical acetylation of histones increases template activity in vitro [Marushige, K. (1976) Proc. Natl. Acad. Sci. USA 73, 3937-3941]. Acetylation was found to have dramatic effects on the magnesium solubility, nuclease sensitivity, thermal denaturation, and sedimentation of chromatin and nucleosomes. The significance of the results to models of gene activation and chromatin replication is considered.

Acetylation↗
PubMed1977

Pea histones H2A and H2B. Variable and conserved regions in the sequences.

Pea histone II group, a mixture of H2A and H2B obtained by chromatography on an ion-exchange resin, was further fractionated by carboxymethylcellulose chromatography and purified by Bio-Gel P-60 chromatography. Their chromatographic behaviors and gel electrophoretic mobilities of single bands differed significantly from those of calf H2A and H2B. Their amino acid compositions were similar to those of the calf histones as a whole, but differed in detail in certain respects. The partial sequence of pea H2B was deduced from the amino acid compositions of BrCN cleavage fragments and tryptic peptides in comparison with the known sequence of calf H2B. It is different in the amino-terminal basic region from the calf H2B, with a blocked amino terminal and a larger number of residues. In contrast, the middle and carboxy-terminal hydrophobic regions are relatively similar, with at least 19-21 different residues and microheterogeneity at two positions of the pea sequence. The sequence of H2A may vary in much the same way as that of H2B, as suggested by the similar extent of differences in their amino acid compositions. It is thus assumed that the amino-terminal regions, at least, of H2A and H2B histones are variable in evolution provided that they remain basic enough to bind DNA, whereas the middle and carboxy-terminal hydrophobic regions of H2A, H2B, H3, and H4 should be conserved to ensure precise histone core formation inside the repeated units of chromatin.

Amino Acid Sequence↗
PubMed1976

Sequence composition of the template-active fraction of rat liver chromatin.

Rat liver chromatin has been separated into nuclease-sensitive and -resistant fractions after mild digestion with DNAase II. The nuclease-sensitive material is further fractionated into Mg2+ -soluble and -insoluble chromatin fractions. The kinetics of production of these chromatin fractions have been investigated. After a brief enzyme treatment (5 min at 10 enzyme units/A260 unit of chromatin at pH 6.6), 11% of the input chromatin DNA is found in the Mg2+ -soluble fraction. This DNA has a weight-average single-strand length of about 400 nucleotides and, as determined by renaturation kinetics, comprises a subset of nonrepetitive DNA sequences and a subset of families of middle repetitive sequences. This demonstrates the nonrandom distribution of repetitive and single copy sequences in the Mg2+ -soluble fraction of chromatin. Previous studies have shown that the Mg2+ -soluble fraction is enriched in nonrepeated sequences which are transcribed in vivo (Gottesfeld, J.M., Garrard, W.T., Bagi, G., Wilson, R.F., and Bonner, J. (1974), Proc. Natl. Acad. Sci. U.S.A. 71, 2193-2197). We now report that the Mg2+ -soluble fraction of liver chromatin contains a low proportion of sequences in common with the Mg2+ -soluble fraction of brain chromatin. Thus, fractionation does not depend on some general property of chromatin but is specific with regard to the template activity of the tissue from which the chromatin was obtained.

Animals↗
PubMed1975

DNA-protein interactions of the rat liver non-histone chromosomal protein.

Native rat liver NHC protein-DNA interactions have been investigated by use of a nitrocellulose filter assay sensitive in detection of protein-DNA complexes. Optimal conditions for DNA-protein interactions occurs at low ionic strength conditions (110 mM phosphate buffer). A fraction of NHC proteins was enriched 25-fold by their affinity for rat DNA immobilized on cellulose columns under these conditions. At higher ionic strength (260 mM-0.04M phosphate buffer and 0.15 M sodium chloride), this fraction binds approximately sevenfold less to rat DNA but with a substantial increase in stability of the complexes. Equilibrium competition experiments indicate that at the higher ionic strength there is a considerable DNA sequence specificity of the rat DNA binding NHC protein. Since rat DNA contains three components as defined by their reassociation kinetics: single copy DNA (C0t1/2pure = 1.6 times 103); middle repetitive DNA (C0t1?1PURE = 1.1); and highly repetitive (C0t1/2pure smaller than 0.02). The two former were isolated and employed in the DNA binding assays. At the high ionic strength criterion, the rat DNA binding NHC proteins showed a substantial preference for a subset of middle repetitive DNA sequences. This suggests a preferential interaction between a class of NHC proteins and a class of middle repetitive DNA sequences.

Animals↗
PubMed1975

DNA-binding proteins from Novikoff hepatoma cells.

In 0.05 M NaCl, 6-8% of the total soluble proteins from Novikoff hepatoma cells bind rapidly and reversibly to columns containing either heterologous or homologous DNA adsorbed to cellulose. These proteins can be eluted by buffer containing 2.0 M NaCl. 0.5-1% of the total protein exhibits a 7-17-fold preference for rat DNA over Escherichia coli DNA. 1-1.5% of the proteins bind DNA so strongly that elution cannot be effected by 4.0 M NaCl but can be accomplished by deoxyribonuclease I treatment of the columns. DNA-binding proteins eluted by 2.0 M NaCl were labeled with 125I or 131I and characterized by sodium dodecylsulfate-polyacrylamide gel electrophoresis and isoelectric focusing. These experiments indicate that DNA-binding proteins represent a discrete subset of the total soluble protein. Many similarities were noted between the major components of the homologous and heterologous DNA-binding fractions.

Animals↗
PubMed1975

Preliminary evidence for the effects of environmental complexity on hybridization of rat brain RNA to rat unique DNA.

Hybridization to unique DNA by RNA from brain or liver of rats given varying degrees of experience was investigated. RNA from brain of environmentally enriched rats hybridized to more unique DNA than did brain RNA from nonenriched controls. No significant differences were observed with liver RNA. This provides preliminary evidence for an increased transcription of the unique sequences of DNA in the enriched animals. The technique used has great promise for the investigation of experientially-induced alterations in gene expression.

Animals↗
PubMed1975

Major nonhistone proteins of rat liver chromatin: preliminary identification of myosin, actin, tubulin, and tropomyosin.

Two major nonhistone polypeptides from rat liver chromatin have been identified as myosin and actin. Preliminary observations indicate that three other chromatin polypeptides of molecular weights 50,000, 34,000, and 32,000 are tubulin and heavy and light tropomyosin, respectively. A sixth component of molecular weight 65,000 which has been purified and electrophoreses as a single band on sodium dodecyl sulfate-polyacrylamide gels may be composed in part of protease-digested myosin. These six polypeptides together account for as much as 38% of the nonhistone protein mass of chromatin in this tissue.

Actins↗
PubMed1975

Structure of transcriptionally active chromatin.

Rat-liver chromatin has bee fractionated into transcriptionally active and inactive regions [Gottesfeld et al. (1974) Proc. Nat. Acad. Sci. USA 71, 2193-2197] and the distribution of nuclease-resistant complexes in these fractions has been investigated. About half of the DNA of both fractions is resistant to attack by tne endonuclease DNase II. The nuclease-resistant structures of inactive chromatin are DNA-histone complexes (v-bodies) which sediment at 11-13 S. Template-active chromatin yields two peaks of nuclease-resistant nucleoprotein. These complexes sediment at 14 and 19 S, and contain DNA, RNA, histone, and nonhistone chromosomal proteins. Polyacrylamide gel electrophoresis reveals a complex pattern of chromatin proteins, suggesting that the complexes are heterogeneous in composition.

Animals↗