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S Varrone

Publications and source records attributed to S Varrone.

At least 37 records · Page 2Linked to original sources
PubMed1978

[In vitro expression of the thyroid gland genome. Difference between chromatin and DNA].

In vitro, transcription by thyroid chromatin has been compared to that carried out by deproteinized DNA prepared from the same tissue. The chromatin-primed transcripts are represented by 4S and 10S RNAs, whereas the DNA-primed transcript is heterogenous and polydisperse. The sequences expressed in vitro have been analyzed by hydridization of 4S and 10S RNA to the total native thyroid DNA. Most of the sequences transcribed are represented by intermediate repetitive-associated an unique sequence. Furthermore, they are expressed only by chromatin and not by DNA. Thus, thyroid chromatin very likely holds in vitro the same fonctional restriction exhibited in vivo, whereas the transcriptional behaviour of thyroid DNA is totally aspecific.

Animals↗
PubMed1978

[Guanyl cyclase in Escherichia coli. II. Identification and characteristics on the enzyme inhibitor].

The activity of guanylate cyclase and that of its inhibitor present in E. coli extract, have been separated through a linear KCl gradient on DEAE-cellulose column. The activity of the inhibitor is lost after ribonuclease treatment, whereas is strengthened by addition of poly (C). Other types of RNA synthetic homopolymers do not affect the inhibitor's activity. Chromatographic analysis of the products of guanylate cyclase measured in the presence of FI and FI plus poly (C), indicated that the inhibitor has a poly (C) dependent GTPase activity.

Deoxyribonucleases↗
PubMed1978

[Guanylate cyclase in E. coli. III. Purification and possible physiological role of GTPase].

A phosphohydrolase with a preferential activity for GTP has been isolated and partially purified from E. coli extracts. The enzyme purification has been achieved through precipitation by ammonium sulfate and chromatography on DEAE-cellulose, DEAE-Sephadex, Ultragel and a second DEAE-cellulose column. The phosphohydrolase activity is poly (C) dependent. The chromatographic analysis on PEI-cellulose has shown that the main product of GTP hydrolysis is GDP. The possibility that the enzyme partially purified in this work has an important role in the control of GTP availability as substrate for guanylate cyclase into the cells has been discussed.

Chromatography, DEAE-Cellulose↗
PubMed1977

Repetitive and non-repetitive sequences in the transcript in vitro of porcine thyroid chromatin.

Purified pig thyroid chromatin has been transcribed in vitro with Escherichia coli RNA polymerase. The transcript, analyzed by DNA-RNA hybridization, shows two major kinetic components: 40% of the transcript is copied by repetitive sequences present 100 times per haploid genome; another 25% anneals to DNA with a rate constant Kh 10-4 M - S-1, typical of single-copy sequences. The transcript annealed at cot = 40 M - S to fractions of 2000-nucleotide DNA, when banded in neutral CsCl gradient only hybridizes to the heavy side of the main band. At cot = 3000 M - S, another hybridizing fraction appears on the light side of the main band of the gradient. The reassociation properties of these fractions show that the heavy DNA fraction is reiterated about 100 times per haploid genome, whereas the light DNA appears as a unique sequence, associated to small repetitive elements. The transcript, analyzed by formamide/sucrose gradient, shows two peaks with sedimentation coefficients of 10 S and 4 S, respectively. The 10-S RNA, hybridized to native 2000-nucleotide-length DNA, has a Kh of 10-4 M - S-1 and a cot1/2 of 10(3) M - S, typical of single-copy sequences.

Animals↗
PubMed1977

Phosphofructokinase (isozymes) activation by theophylline or by 3',5' cyclic AMP administration.

Phosphofructokinase activity of rat thyroid, kidney and muscle can be enhanced by in vivo administration of theophylline or cyclic AMP. This enhancement occurs in the different tissues to a different extent depending on the tissue-specific isozymes. Thyroid and muscle phosphofructokinase which is mainly A-type, is strongly stimulated after administering theophylline in the drinking water over a 8 days period. The kidney enzyme which encompasses about 50% of each A and B type is activated to a lesser extent. Liver phosphofructokinase which is pure B-type shows very little response if any. Comparable results have been obtained with either the muscle or liver enzyme after two to four hours treatment with a single injection of 10 mg/rat of either cyclic AMP or theophylline. This short-term activation could be eliminated by treating the animals with Actinomycin D, 30 min prior to theophylline or cyclic AMP. The possible mechanisms leading to the enhancement of phosphofructokinase activity are discussed.

Animals↗
PubMed1977

[Guanyl cyclase activity in the EF-T elongation factor of Escherichia coli].

Highly purified EF-Ts from E. coli does contain guanylate cyclase activity, which is absent from other purified transfer factors, such as EF-Tu and EF-G. Guanylate cyclase activity has been characterized by its sensitivity to inhibitors and substrate specificity. Although the physicochemical properties of guanylate cyclase are closely related to those of EF-Ts, it does not appear to be a contaminant of this transfer factor, but a specific enzyme. The possible role of guanylate cyclase in protein synthesis is discussed.

Aurintricarboxylic Acid↗
PubMed1976

Sequence organization of porcine DNA.

The sequence organization of porcine DNA isolated from thyroid has been analyzed by hydroxylapatite (HAP) chromatography. The reassociation of 0.4 kilobase (Kb) DNA fragments shows, besides the presence of 5% inverted repeat sequences (foldback DNA), that 45% of the genome is represented by high (10%) and intermediate (35%) repetitive components, whereas the remaining 50% is unique sequences. 30% of the unique sequences consists of 1,000 nucleotide fragments interspersed with repetitive elements 400 nucleotides in length. The remaining 20% is longer unique sequences (10,000 nucleotides) apparently not linked to repetitive elements.

Animals↗
PubMed1975

Guanylate cyclase in Escherichia coli. Purification and properties.

Guanylate cyclase has been purified from extracts of Escherichia coli. After a 1000-fold purification, the enzyme contains only minor contaminants as judged by disc gel electrophoresis. The Km for GTP is approximately 7 times 10(-5) M and the optimal pH is 8.0. More activity is observed with Mn2+ than with Mg2+, and maximal activity is observed at 0.14 mM Mn2+ and 1.4 mM Mg2+. Based on its behavior on Sephadex G-100, the molecular weight of E. coli guanylate cyclase is about 30,000. Disc gel electrophoretic analysis indicates that the enzyme consists of a single polypeptide chain. Guanylate cyclase does not form 3':5'-AMP from ATP, and therefore, is distinct from adenylate cyclase.

Enzyme Activation↗
PubMed1975

In vitro synthesis of a thyroglobulin precursor by porcine thyroid membrane-bound ribosomes in a heterologous cell-free system.

The synthesis of a thyroglobulin precursor directed by endogenous messenger RNA has been achieved in a heterologous cell-free system containing porcine thyroid membrane-bound ribosomes and rat brain cortex cell sap. The main features of the system, such as ion and nucleotide requirements, temperature, dependence, inhibitors sensitivity, and ability to reinitiate, were studied. The nature of the product has been determined by specific immunoprecipitation and its size has been estimated by sucrose density gradient and sodium dodecyl sulfate acrylamide gel electrophoresis. Under our conditions, the thyroglobulin precursor was mainly synthesized by membrane-bound ribosomes.

Animals↗