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H Cedar

Publications and source records attributed to H Cedar.

At least 109 records · Page 6Linked to original sources
PubMed1976

RNA chain elongation on a chromatin template.

The rate of RNA chain elongation has been measured with DNA and chromatin as template. RNA propagation on chromatin is about 50% of the rate found with DNA. Kinetic experiments demonstrate that the inhibition is not due to interference with the addition of the nucleoside triphosphates. Analysis of the dependence of propagation on the Tm of DNA shows that the chromatin proteins interfere with the translocation of the RNA polymerase along the DNA template.

Animals↗
PubMed1976

Annealing and hybridization properties of herpes simplex virus type 1 DNA.

The hybridization properties of the herpes simplex virus type 1 (HSV) genome have been analysed. The DNA has a kinetic complexity of 1 X 10(-8). E. cole RNA polymerase was found to initiate synthesis at about 70 sites on the HSV DNA. The in vitro RNA product from this reaction was complementary to about 80% of the HSV genome. The RNA-DNA hybridization rate constant (Kh) was determined using conditions of both RNA excess and DNA excess. Using this rate constant one can analyse the content of HSV sequences in any RNA population.

Base Sequence↗
PubMed1975

The structure of the globin genes in chromatin.

The distribution of proteins in the neighborhood of the globin genes of duck reticulocyte chromatin has been studied. This chromatin is first shown to be an active template for transcription in vitro of globin messenger-like RNA. The chromatin is then treated with staphylococcal nuclease and the DNA fragments protected from nuclease attack ("covered DNA") are isolated. Alternatively, the chromatin is titrated with poly-D-lysine, and by successive treatment with Pronase and nuclease, the DNA regions accessible to polylysine are isolated (open "DNA"). In order to determine the distribution of globin gene sequences in open and covered DNA, these two fractions are annealed to globin cDNA (globin probe). It is found that while all globin gene sequences are represented in covered DNA, a specific portion of the globin gene is missing from open DNA, corresponding to about 20% of the gene length. It is concluded that specific regions of the globin genes of reticulocyte chromatin are partly covered by proteins in such a way as to render them in accessible to polylysine. In contrast, no difference is observed in the annealing properties of open and covered regions to globin probe using DNA isolated from erythrocyte chromatin, which is a poor templete in vitro for production of globin message. The annealing of open and covered DNA to each other has also been studied. It is found that open and covered DNA have identical sequence populations. Thus, in contrast to the special arrangement of proteins in the neighborhood of the globin gene, there does not appear to be any sequence-specific arrangement of the bulk of the chromatin proteins on chromatin DNA.

Adenosine Triphosphate↗
PubMed1975

Metabolism of acetylcholine in the nervous system of Aplysia californica. I. Source of choline and its uptake by intact nervous tissue.

Although acetylcholine is a major neurotransmitter in Aplysia, labeling studies with methionine and serine showed that little choline was synthesized by nervous tissue and indicated that the choline required for the synthesis of acetylcholine must be derived exogenously. Aanglia in the central nervous system (abdominal, cerebral, and pleuropedals) all took up about 0.5 nmol of choline per hour at 9 muM, the concentration of choline we found in hemolymph. This rate was more than two orders of magnitude greater than that of synthesis from the labeled precursors. Ganglia accumulated choline by a process which has two kinetic components, one with a Michaelis constant between 2-8 muM. The other component was not saturated at 420 muM. Presumably the process with the high affinity functions to supply choline for synthesis of transmitter, since the efficiency of conversion to acetylcholine was maximal in the range of external concentrations found in hemolymph.

Acetylcholine↗
PubMed1973

Synthesis of globin ribonucleic acid from duck-reticulocyte chromatin in vitro.

The proteins of chromatin serve to restrict the transcription of DNA. The relevance of these findings to the control of gene expression is contingent upon the demonstration that this restriction is specific and mirrors the patterns of RNA synthesis observed in vivo. In this study we demonstrate by RNA-DNA hybridization that the vast majority of the chromatin-directed RNA is synthesized from the unique regions of the reticulocyte genome. Furthermore, by use of the DNA complement of globin mRNA as a probe in annealing reactions, de novo synthesis of globin RNA was detected in RNA transcripts from duck reticulocyte chromatin. No globin sequences were detected in similar preparations of RNA in vitro either from liver chromatin or from DNA freed of protein. These results show that the proteins of chromatin serve to restrict transcription in a very specific manner and provide convincing evidence for the existence of transcriptional control factors in eukaryotes.

Animals↗
PubMed1972

Cyclic adenosine monophosphate in the nervous system of Aplysia californica. I. Increased synthesis in response to synaptic stimulation.

In the isolated abdominal ganglion of Aplysia, previously incubated in adenine-(3)H, the amount of (3)H-labeled adenosine-3',5' monophosphate (cAMP) doubled after electrical stimulation of nerves at a physiological rate (1/sec). No change was detected after 4 min of stimulation. An increase in cAMP was first seen after 15 min; lengthening the period of stimulation to 1 hr did not increase the extent of the effect. ATP contained 50% of the total radioactivity taken up from adenine-(3)H, cAMP about 0.1%. During stimulation both the total amount and the specific radioactivity of adenosine triphosphate (ATP) did not change. Thus, the increased amount of radioactivity found in cAMP after stimulation represented an increase in its rate of synthesis. During stimulation formation of cAMP-(3)H was not altered in nerves or in the cell body of an identified neuron (R2). In addition, no changes were detected in the total amounts of cAMP in the ganglion and in the cell body of R2. It seems likely that the increase was initiated by synaptic activity rather than by action potentials. It was blocked by elevating the concentration of Mg, which also blocks synaptic activity without impairing conduction of impulses. Moreover, impulse activity induced by ouabain and glutamate did not result in increased formation of cAMP.

Action Potentials↗
PubMed1972

Cyclic adenosine monophosphate in the nervous system of Aplysia californica. II. Effect of serotonin and dopamine.

Serotonin and dopamine, both likely transmitter substances in Aplysia, stimulated formation of adenosine-3',5' monophosphate (cAMP) in ganglia, connectives, and identified nerve cell bodies. This widespread distribution suggests that receptors for the response are localized throughout the nervous system, as is adenyl cyclase. Both synthesis of cAMP-(3)H from precursor previously labeled in incubations with adenine-(3)H and total content of cAMP were stimulated up to 15-fold. The acetylcholine analogue carbachol, glutamate, norepinephrine, and histamine were inactive. Full stimulation occurred within 2-4 min of applying serotonin; the extent of the effect was half maximal at 6micro serotonin. Even in the continued presence of serotonin, the increased cAMP diminished with time. When serotonin was removed, tissue remained refractory for 15-20 min; sensitivity returned after 25 min. Serotonin stimulated cAMP after removal of extracellular Na, K, or Cl and in isotonic sucrose, with all extracellular ions removed. Elevating Mg, which blocked the stimulation of cAMP caused by synaptic activity, did not affect the response to serotonin. Thus the response appeared to be independent of transmitter release and of changes in synaptic potentials and current flow. The role of cAMP in neuronal functioning remains to be determined. Conditions which markedly increased cAMP in neurons, however, did not affect the rate of RNA synthesis, nor did they alter the distribution of phosphorylated adenine or uridine nucleotides.

Action Potentials↗
PubMed1968

Production of L-asparaginase II by Escherichia coli.

l-Asparaginase II was synthesized at constant rates by Escherichia coli under anaerobic conditions. The enzyme was produced optimally by bacteria grown between pH 7 and 8 at 37 C. Although some enzyme was formed aerobically, between 100 and 1,000 times more asparaginase II was produced during anaerobic growth in media enriched with high concentrations of a variety of amino acids. Bacteria grown under these conditions should provide a rich starting material for the large-scale production of the enzyme. No single amino acid specifically induced the synthesis of the asparaginase, nor did l-asparagine, even when it was used as the only source of nitrogen. The enzyme was produced at lower rates in the presence of sugars; glucose was the most inhibitory.

Amino Acids↗
PubMedDate not supplied

In situ nick-translation distinguishes between active and inactive X chromosomes.

Template-active regions of chromatin are structurally distinct from nontranscribing segments of the genome. Recently, it was suggested that the conformation of active genes which renders them sensitive to DNase I may be maintained even in fixed mitotic chromosomes. We have developed a technique of mitotic cell fixation and DNase I-directed nick-translation which distinguishes between active and inactive X chromosomes. We report here that Gerbillus gerbillus (rodent) female cells contain easily identified composite X chromosomes each of which includes the original X chromosome flanked by two characteristic autosomal segments. After nick-translation the active X chromosome in each cell is labelled specifically in both the autosomal and X-chromosomal regions. The inactive X chromosome is labelled only in the autosomal regions and in a small early replicating band within the late replicating 'original X' chromosome. Our technique opens the possibility of following the kinetics of X-chromosome inactivation and reactivation during embryogenesis, studying active genes in the inactive X chromosome and mapping tissue-specific gene clusters.

Animals↗
PubMedDate not supplied

Regulated expression of an introduced MHC H-2K bm1 gene in murine embryonal carcinoma cells.

The transplantation antigens H-2K, H-2D and H-2L are developmentally regulated, highly polymorphic cell surface proteins encoded by the major histocompatibility gene complex (MHC). First detectable on the early embryo, they are subsequently expressed on most somatic cells of the adult mouse in association with the protein beta2-microglobulin (beta 2 M; ref. 5). Cultured F embryonal carcinoma (EC) cells can be induced to differentiate along alternative pathways to form either parietal or visceral9 extra-embryonic endoderm, each concomitant with a change in morphology and pattern of gene expression. Previous reports have demonstrated an increased level of transplantation antigens in differentiated F9 EC cells, but the cell types expressing them were not defined. Here we show that the level of MHC H-2Kb and beta 2 M transcripts is increased during both pathways of this differentiation. Expression of a foreign MHC H-2Kbm1 gene was found to be regulated in a similar manner when the gene was introduced into EC cells. In contrast, an introduced rabbit beta-globin gene was not regulated but expressed constitutively.

Animals↗