PubMed Health⌕ Search

Biomedical subjects

R W Barton

Publications and source records attributed to R W Barton.

51 records · Page 3Linked to original sources
PubMed1977

Demonstration of terminal deoxynucleotidyl transferase in thymocytes by immunofluorescence.

The cellular and subcellular distribution of terminal deoxynucleotidyl transferase (DNA nucleotidylexotransferase; nucleosidetriphosphate:DNA deoxynucleotidylexotransferase, EC 2.7.7.31) in thymocytes and peripheral lymphocytes from rat, mouse, and calf was studied by immunofluorescence using rabbit antiserum to homogeneous transferase from calf. Terminal transferase was readily detected in approximately 75% of cortical thymocytes, but not in medullary thymocytes or lymph node lymphocytes. The enzyme appeared to be present predominantly in the cytoplasm of positive thymocytes in ethanol-fixed cell smears and frozen sections. The reactivity of anti-terminal-transferase for thymocytes could be neutralized with purified calf enzyme. Results of experiments in which thymocytes were separated on 7-step discontinuous Ficoll density gradients suggested that cortical thymocytes are heterogeneous with respect to terminal deoxynucleotidyl transferase content.

Animals↗
PubMed1977

Intracellular distribution of terminal deoxynucleotidyl transferase in rat bone marrow and thymus.

A subset of bone marrow cells that contains terminal deoxynucleotidyl transferase (DNA nucleotidylexotransferase; nucleosidetriphosphate:DNA deoxynucleotidylexotransferase, EC 2.7.7.31) can be identified in adult rats by immunofluorescence using affinity-column-purified antibody to homogeneous calf transferase. The transferase-positive cells comprise approximately 1.8% of bone marrow cells. Correcting the specific activity of terminal transferase in total bone marrow cells (0.21 units per 10(8) cells) for the percentage of transferase-positive bone marrow cells (1.8%) gives 11.7 units per 10(8) cells, a value approximately half that found for transferase-positive thymocytes. Fluorescence appears to be restricted to the nucleus of transferase-positive bone marrow cells, in contrast to the predominantly cytoplasmic fluorescence of small thymocytes from adult rats. Some large thymocytes contain intranuclear transferase fluorescence patterns similar to those seen in bone marrow. These thymocytes are especially numerous in neonatal rat thymus, where they are localized in the subcapsular region of the cortex. Thymocytes with combined patterns of nuclear and cytoplasmic transferase are also present. In addition, Thy-1.1 antigen, which is present on thymic and prethymic cells but not on the majority of post-thymic cells in the rat, is also present on transferase-positive bone marrow cells. The results suggest that the transferase-positive subset of bone marrow cells may contain the immediate progenitors of cortical thymocytes in the rat. The nuclear location of fluorescence may indicate the site of physiological activity of terminal transferase in thymocytes and their precursors.

Aging↗
PubMed1971

Interaction between the first enzyme for histidine biosynthesis and histidyl transfer ribonucleic acid.

Previous studies suggested that phosphoribosyltransferase, which catalyzes the first step of the pathway for histidine biosynthesis in Salmonella typhimurium and which is sensitive to inhibition by histidine, plays a role in repression of the histidine operon. Recently, we showed that the enzyme has a high affinity for histidyl transfer ribonucleic acid (His-tRNA), which is known to participate in the repression process. In the present study, we have investigated further the interaction between the enzyme and His-tRNA. We found that His-tRNA binds at a site on phosphoribosyltransferase distinct from the catalytic site and the histidine-sensitive site; that the substrates of the enzyme inhibit the binding of His-tRNA, whereas histidine does not do so; that, once a complex has been formed between phosphoribosyltransferase and His-tRNA, the substrates of the enzyme decrease the stability of the complex, whereas histidine is without effect; and that purified phosphoribosyltransferase which has a defect in its inhibition by histidine (produced by mutation) displays an altered ability to bind His-tRNA, a finding which may be a reflection of the fact that mutants producing such a defective enzyme display an alteration of the repression process.

Acrylates↗
PubMed1970

Interaction between histidyl transfer ribonucleic acid and the first enzyme for histidine biosynthesis of Salmonella typhimurium.

Previous studies showed that the enzyme (phosphoribosyltransferase) which catalyzes the first step of the histidine pathway in Salmonella typhimurium plays a role in regulation of the histidine operon. Since histidyl transfer ribonucleic acid (His-tRNA) is required for repression of the histidine operon, we considered the possibility that the role of phosphoribosyltransferase might be realized through an interaction with His-tRNA. One prediction inherent in this idea is that the enzyme should interact with His-tRNA in vitro. Evidence is presented for such an interaction. Binding of (3)H-His-tRNA to purified phosphoribosyltransferase was tested on Sephadex columns and on nitrocellulose filters. The enzyme was found to have a high affinity for tRNA. Comparing the binding of (3)H-His-tRNA with that of tRNA aminoacylated with other (3)H-amino acids disclosed that the binding of the histidyl species of tRNA is favored over that of other species and is dependent upon magnesium-ion concentration.

Acrylates↗
PubMedDate not supplied

Low molecular weight DNA polymerase: decreased activity in spleens of old Balb/c mice.

The DNA polymerase activities in the spleens of young adult (3-8 months) and senescent (24-30 months) female BALB/c mice have been examined. Comparisons were made by direct assay of activated DNA-dependent and (rA)n-(dT)n-dependent activities in extracts from cytoplasmic and neclear fractions and also by sucrose gradient sedimentation analysis of the two major forms of DNA polymerase activity was equivalent in the spleens of young and old BALB/c mice. The low molecular weight DNA polymerase activity was decreased in the spleens of old BALB/c mice. This decreased activity was reflected most markedly in the nuclear fraction of the spleens. Mixing experiments did not indicate the presence of inhibitors in the nuclear extract from the old mouse spleens. Stepwise extractions of isolated nuclei with increasing NaCl concentrations showed consistent results without revealing any difference in extractability of the low molecular weight DNA polymerase from the old mouse chromatin. Isolated low molecular weight DNA polymerase preparations from the young and old BALB/c mouse spleens are similar in chromatographic migration, sucrose gradient sedimentation, heat lability in vitro and Km of substrates. The low molecular weight DNA polymerase activity was not found to decline in livers and kidneys of 24 to 30-month-old BALB/c mice, nor in spleens of 30 to 34-month-old BC3F1 mice.

Animals↗