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J J Lawrence

Publications and source records attributed to J J Lawrence.

70 records · Page 4Linked to original sources
PubMed1981

Involvement of histone H1 in the structure of the linker DNA in nucleosomes as revealed by nucleases.

This report describes experiments designed to study the organization of the linker DNA in nucleosomes. When rat liver nucleosomes (145 to 188 base pairs in length) were digested by Exonuclease III and then by nuclease S1 a series of bands on sizes 90 - 102 - 112 - 125 - 135 - 142 - 154 - 166 - 172 - 181 - bases was observed in denaturing electrophoretic gels. Digestion of H1-depleted nucleosomes under the same conditions results in a series of products of sizes (10.4) xn in base (n less than or equal to 14) only. This result is interpreted as reflecting a particular arrangement of linker DNA under the influence of histone H1.

Animals↗
PubMed1981

Distribution of linker DNA in relation to core DNA in H1 depleted nucleosomes.

The mode of interaction of histone H1 with the nucleosome is governed by the relative distribution of the linker with respect to the core DNA. Preliminary experiments (Simpson, R.T. 1978, Biochemistry, 17, 5524-5531) and tentative models (Thoma, F. et al. (1979), J. Cell. Biol., 83, 403-427) suggest that part of the linker complete two full turns of DNA around the histone core, probably by adding 10 base pairs at each end of the core DNA. In the present study Exonuclease III has been utilized to digest the 3' ends of H1 depleted nucleosomes. (i.e. the 195 base pair particle). The analysis of the resulting DNA fragments under denaturing conditions shows that the whole linker is distributed symmetrically with respect to the core DNA.

Animals↗
PubMed1980

Selective removal of histone H1 from nucleosomes at low ionic strength.

The method for removal of histone H 1 from chromatin by treatment with ion-exchange resin AG 50 WX 2 in the presence of 100 mM NaCl and 50 mM phosphate buffer (Thoma and Koller, 1977, Cell, 12, 101-107) results in production not only of H1-depleted chromatin but also free DNA. We have not modified this procedure so that the nucleosome is treated with the cation exchange resin in two steps, first in 50 mM sodium phosphate buffer and then in 50 mM sodium phosphate and 50 mM NaCl whereby histone H 1 is selectively removed without a release of free DNA at low resin concentrations.

Cation Exchange Resins↗
PubMed1980

Spin-label study of histone H1-DNA interaction. Comparative properties of the central part of the molecule and the N and C-amino tails.

Covalent spin labelling of lysine and arginine residues in histone H1 under specified conditions allows the study of histone-DNA interaction. When the labelled histone is free in solution, the electron spin resonance spectrum is characteristic of a label moving in a viscous medium while the label becomes fully immobilized upon the interaction of histone and DNA. This property is used to study histone-DNA interactions under various conditions of ionic strength and thermal denaturation. On the other hand, spin label probes in the globular part of the molecule shows no strong immobilization upon binding to linear DNA, suggesting a special mechanism for the binding of histone H1 to chromatin.

Animals↗
PubMed1979

Experimental evidence for asymmetrical shielding of nucleosomal DNA by histones.

Electron spin resonance study of Mn (II) binding to chromatin and derivatives, including core particles, shows that Mn (II) is a good probe for testing the overall electrostatic balance of the nucleoproteic complex as well as DNA accessibility. Experimental results are in good agreement with a recent model proposed (Mirzabekov A. D. and Rich A. (1979) Proc. Natl. Acad. Sci. USA 76, 1118-1121), for the core particle, in which an asymmetrical shielding of DNA by the protein core is assumed. Furthermore, it was found that the histone H1 hinders a number of charges on the linker DNA in a proportion equal to the net positive charge of the histone itself. This result is interpreted as due to a tighter interaction between the linker DNA and the core histones in the presence of histone H1.

Animals↗
PubMed1979

The distribution of histone H1 subfractions in chromatin subunits.

Rat liver chromatin was digested with micrococcal nuclease to various extents and fractionated into nucleosomes, di and trimers of nucleosomes on an isokinetic sucrose gradient. In conditions under which degradation of linker DNA within the particles was limited, the electrophoretic analysis of the histone content showed that the overall content of H1 histone increased from nucleosomes to higher order oligomers. Moreover, the histone H1 subfractions were found unevenly distributed among the chromatin subunits, one of them, H1--3 showing most variation. A more regular distribution of these subfractions was found in subunits obtained from a more extended digestion level of chromatin. It is suggested that the H1 subfractions differ in the protection they confer upon DNA.

Animals↗
PubMed1978

Clinical evaluation of freeze-dried bone allografts in periodontal osseous defects--part II.

Freeze-dried crushed cortical bone allografts were implanted into widemouthed three-wall, two-wall, one-wall, combination, and furcation defects. One hundred eighty-nine sites were reentered in 97 patients and of these 60% had osseous regeneration of greater than 50%. A total of 231 sites were evaluated for pocket elimination, of which 63% demonstrated greater than 50% pocket reduction. This study presented additional evidence indicating that freeze-dried bone allografts have definite potential as grafting material in certain periodontal osseous defects. Information from additional cases is being tabulated as it becomes available and will supplement the current data.

Adult↗
PubMed1976

Ethidium bromide as a probe of conformational heterogeneity of DNA in chromatin. The role of histone H1.

The accessibility and the tertiary structure of the DNA inside chromatin were studied by using ethidium bromide (EB) as a fluorescent probe. The exclusion model of binding was refined by introductina a parameter alpha (0less than alpha less than 1) which measures the accessibility of the DNA and by taking into account when necessary the existence of two sets of binding sites. We were thus able to fit predicted and experimental isotherms and then to describe completely EB binding to native or partially histone depleted chromatin under various conditions. Itn native chromatin 95% of the DNA (alpha = 0.95) appears to be accessible to EB but two sets of sites are present. The first one corresponds to alpha = 0.13 and is characterized by an affinity constant which is higher by two orders of magnitude than that relative to pure DNA. The second set corresponds to alpha = 0.82 and the corresponding binding constant is only three or four times lower than that of pure DNA. The sites with high affinity are still present after treatment with formaldehyde but disappear after removal of histon H1. By comparison with chromatin treated with deoxycholate of with artifical complexes between H1 and DNA, high affinity sites were found only when all of the histons are bound to DNA. An alpha value around 0.8 is still obtained in 1 M NaC1 treated chromatin, pointing to the fact that histones H3 and H4 are preventing 20% of the DNA to intercalate EB.

Binding Sites↗
PubMed1976

Conformational state of DNA in chromatin subunits. Circular dichroism, melting, and ethidium bromide binding analysis.

This study compares some physical properties of DNA in native chromatin and mono-, di-, trinucleosomes obtained after mild micrococcal nuclease digestion. Melting curves and derivatives are shown to be very similar from one sample to another although a shift from 79 to 82 degrees C is observed between the mainly monophasic peak of multimers and chromatin. Careful analysis of the positive band of the circular dichroism spectra shows the appearance of a shoulder at 275nm, the intensity of which increases from the mono- to the di- and trinucleosome. This shoulder is maximum for native chromatin. At the same time binding isotherms of ethidium - bromide are characterized by two highly fluorescent binding sites for all the samples but the product KN of the apparent binding constant of the higher affinity binding sites by the apparent number of those sites increases from the mono- to the di- and trinucleosome. There again the valus is maximum for native chromatin. Such results strongly suggest that the native state of chromatin requires something more than the indefinite repeat of an elementary subunit.

Animals↗
PubMed1976

A clinical study of healing in humans following the excisional new attachment procedure.

The excisional new attachment procedure was used to treat 75 suprabony pockets on 32 teeth in 9 patients. One-year postoperative measurements demonstrated an overall mean pocket reduction from 4.7 mm to 2.0 mm, of which 2.1 mm (77%) was new attachment and 0.6 mm was recession. Average amount of new attachment and percentage of new attachment were greatest on the midlingual surfaces of the teeth treated in this study. The results of this study showed the excisional new attachment procedure to be a simple, effective, and predictable procedure for achieving pocket elimination by means of a clinical new attachment of the gingival tissues in suprabony pockets.

Epithelial Attachment↗
PubMed1976

Clinical evaluation of freeze-dried bone allografts in periodontal osseous defects.

Freeze-dried cortical bone allografts of a fine particle size were implanted into wide three-wall, two-wall, one-wall, combination, and furcation defects. Of the 97 defects treated, 23 manifested complete bone regeneration; 39 showed greater than 50%; and 24, less than 50% osseous repair. Twelve defects failed to demonstrate any bony regeneration, of which nine were furcation involvements. From the preliminary data available, there is strong evidence which indicates that freeze-dried bone allografts have definite potential as grafting material in certain periodontal osseous defects. However, final determination must await the outcome of a larger number of cases and also histologic evidence.

Adult↗
PubMedDate not supplied

Association of histone H1(0) with a gene repressed during liver development.

Histone H1(0) has a number of unusual properties that set it apart from other H1 subtypes (for review see ref. 1). For example, H1(0) synthesis is not strictly coupled to DNA synthesis, it is absent from the embryonic liver of mice (but present shortly after birth) and its synthesis is hormone-dependent in some of the glands of adult rodents. All the H1 subtypes differ in their DNA binding properties, and H1(0) has been shown to be preferentially associated with nuclease-resistant chromatin. These features suggest that the H1(0) may have a role in developmental gene control. To investigate this further, we have fractionated the H1(0)-containing nucleosomes of chromatin from adult mouse liver. We report here that the gene for alpha-fetoprotein, which is expressed in embryonic tissue but repressed soon after birth, is preferentially associated with the H1(0)-containing nucleosomes. The related gene for albumin, which is expressed in both embryonic and adult tissues, is absent from the H1(0)-containing nucleosome fraction. These results support a role for histone H1(0) in the control of gene expression.

Albumins↗
PubMedDate not supplied

Selective cytotoxicity of L-glutamic acid gamma-monohydroxamate (GAH) for melanoma tumor cells.

We have previously shown that L-glutamic acid gamma-monohydroxamate (GAH) exhibits an antitumor activity, both in vitro and in vivo. In this report we explore the selective cytotoxicity of GAH in vitro by comparing the survival of tumor and normal cells. GAH exerts an irreversible delayed effect with tumoral cells and a reversible effect with normal cells: after a short incubation time of 6 hrs in the presence of 1.2 mM GAH and after removal of the drug, the survival of N Ter Dau and MRC5 cells was identical reaching about 85% after 24 hrs of culture. But, after another 48 hrs of culture, MRC5 cells recovered 100% cell survival while with N Ter Dau cells the survival decreased to 65%. A longer exposure time to GAH (18 hrs) and an additional 54 hrs of culture after removal of GAH led to 50 +/- 10% of cell survival with normal cells but only 25 +/- 10% with tumor cells. Using a long-term clonogenic assay, we showed that the 25% N Ter Dau cells surviving at 72 hrs after GAH treatment led mainly to abortive colonies (17% +/- 3%) with only 2.3 +/- 0.9% of surviving colonies. Such a difference does not exist for normal cells. Cell cycle analysis of tumor and normal cells treated with GAH (18 hrs, 1,2 mM) has shown that the drug prevents both cell type from cycling from G1 to S phase. However, the two cell types started to cycle again after removal of GAH but a delay of 24 hrs was observed for tumoral cells compared to normal cells.

Animals↗