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Biomedical subjects

W M Bonner

Publications and source records attributed to W M Bonner.

At least 73 records · Page 4Linked to original sources
PubMed1978

Proximity and accessibility studies of histones in nuclei and free nucleosomes.

Histone proximity in chromatin was studied with the cleavable crosslinking reagent, dithiobissuccinimidyl propionate. Crosslinks between H4 and H2a, H4 and H2b, H4 and H3, H2a and H2b, H2b and H3 were found. H1 is also crosslinked to the nucleosomal histones. In nuclei, unsheared chromatin, and H1 depleted chromatin, the four nucleosomal histones are crosslinked at similar relative rates both in 5 mM salt and 100 mM salt. After micrococcal nuclease treatment to generate nucleosomes, H2a and H2b are crosslinked faster than H4 and H3. C14-NEM titration of thiopropionate residues bound to each histone shows that H2a and H2b are more accessible to this reagent after nuclease treatment but that the increased binding was not sufficient by itself to explain the increase in crosslinking. Bolton Hunter reagent was used to further study the accessibility of the four nucleosomal histones in whole chromatin and nuclease digested chromatin. These studies showed that salt increases the accessibility of all four histones while nuclease treatment decreases H4 accessibility.

Animals↗
PubMed1975

Protein migration into nuclei. I. Frog oocyte nuclei in vivo accumulate microinjected histones, allow entry to small proteins, and exclude large proteins.

A technique is presented which enables one to measure the extent to which a protein enters and accumulates in the nucleus of the frog oocyte. In this method, the protein, labeled with 125-I, is microinjected into the oocyte. After incubation, the oocyte is manually enucleated and the radioactivity in the nucleus and cytoplasm is determined. Using this technique, proteins lighter than 20,000 daltons were found to enter the nucleus and completely equilibrate between the nucleus and cytoplasm within 24 h. The entry of proteins heavier than 69,000 daltons was severely hindered. Histones and histone fractions entered as quickly as other small proteins, but, in contrast to these proteins, they accumulated in the nucleus to different extents, depending on the total amount of histone injected into the oocyte and the identity of the histone. Evidence is presented that histone fractions compete with each other for accumulation in the nucleus.

Animals↗
PubMed1975

Protein migration into nuclei. II. Frog oocyte nuclei accumulate a class of microinjected oocyte nuclear proteins and exclude a class of microinjected oocyte cytoplasmic proteins.

Nuclear contents or cytoplasm from Xenopus oocytes labeled with (35-S)methionine or (3-H)proline (donor oocytes) were reinjected into unlabeled oocytes (recipient oocytes). The radioactivity injected as nuclear contents was found to enter and accumulate in the recipient oocyte nucleus. In contrast, the radioactivity injected as cytoplasm was found to enter but not to accumulate in the recipient oocyte nucleus. Sodium dodecyl sulfate (SDS) gel electrophoresis of the nucleus and cytoplasm of donor oocytes revealed the existence of three classes of labeled proteins in these oocytes: those proteins found predominantly in the nucleus (N proteins), those found predominantly in the cytoplasm (C proteins), and those found in both the nucleus and cytoplasm at similar concentrations (B proteins). SDS gel electrophoresis of the nucleus and cytoplasm of recipient oocytes showed that N proteins entered and accumulated in the nucleus but that B proteins partitioned about equally between the nucleus and cytoplasm. A similar analysis of oocytes injected with labeled cytoplasm showed that C proteins did not enter the nucleus but again B proteins partitioned about equally between the nucleus and cytoplasm.

Animals↗
PubMedDate not supplied

Changes in the lipids of human articular cartilage with age.

Histochemical and chemical studies demonstrated a significant increase in the lipods of articular cartilage with advancing age. Triglycerides, cholesterol, and phospholipids were identified chemically and were shown by comparative staining procedures to be present in intracellular and extracellular lipids. The distribution and the composition of the extracellular lipids were interpreted as indicating that the extracellular lipids are of cellular origin. Glycolipids were extracted from cartilage of all ages and were shown to account for a portion of the increase in total lipid with age. Glycolipids extracted from aged cartilage were partially characterized. Cerebrosides, sulfatides, and gangliosides were detected. Glycolipids were estimated to comprise from 5 to 10% of the total lipid of articular cartilage. Arachidonic acid concentrations increased maredly with age in the surface of cartilage but were present in trace amounts in deep cartilage, demonstrating clear-cut differences in the levels as well as the location of this fatty acid precursor of the prostaglandins (PGE2 and PGF2alpha).

Adolescent↗