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Biomedical subjects

S Spadari

Publications and source records attributed to S Spadari.

At least 127 records · Page 7Linked to original sources
PubMed1977

Variation of DNA polymerases-alpha, -beta. and -gamma during perinatal tissue growth and differentiation.

The activities of the three known DNA polymerases-alpha, beta-, and -gamma were determined in rat brain neurons, cardiac muscle and spleen, and were correlated with the rate of cell proliferation during perinatal development. In neurons and cardiac muscle, which stop dividing before birth, DNA polymerase-alpha activity drops sharply from a high level with the approach of term and disappears at approximately two weeks postnatal age. In contrast, alpha-polymerase activity is almost absent in spleen during late gestation, when the rate of cell division is low, and increases abruptly after birth with the sudden onset of cell proliferation. These data give further evidence for an involvement of DNA polymerase-alpha in DNA replication. DNA polymerase-beta and -gamma activities show essentially no correlation with the rate of cell division. Thus, these enzymes are probably responsible for repair type processes rather than for DNA replecation.

Aging↗
PubMed1976

A novel endonuclease of human cells specific for single-stranded DNA.

We have fractionated from human aneuploid cell cultures three different enzyme fractions degrading single-stranded DNA. We have purified and characterized one of these DNases; this is an endonuclease working at alkaline pH (around 9.5) and requiring Mg2+ for its activity. The enzyme degrades denatured DNA over 100 times more efficiently than native DNA in optimal conditions. The termini produced by the enzyme have 5'P and 3'OH ends. The enzyme can attack, though at reduced rate, the supertwisted circular molecule of Simian virus 40 DNA, whereas it is inactive on the nicked circular molecule. The ultraviolet irradiation of DNA, whether native or denatured, does not affect its efficiency as substrate of the DNase. The properties of this endonuclease distinguish it from those of the other DNases described previously in mammalian cells; the denomination DNase VI is therefore proposed. Its properties are similar to those of DNases described in Ustilago maydis and Bacillus subtilis, for which an essential role in recombination seems likely.

Calcium↗
PubMed1976

Variations of DNA polymerase-alpha and -beta during prolonged stimulation of human lymphocytes.

Stimulation of human lymphocytes with phytohemagglutinin is known to induce an increase in overall DNA polymerase activity (DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7). Previous work [Pedrali Noy, G., Dalprà, L. Pedrini, A. M., Ciarrocchi, G., Giulotto, E., Nuzzo, F. & Falaschi, A. (1974) Nucleic Acids Res. 1, 1183] has shown that two subsequent waves of induction of DNA polymerase can be observed in this system; a first wave occurs in parallel with the increase in DNA replication rate; a second one occurs when the DNA synthesis rate is returned to minimal levels; the second peak is parallel to a maximum in DNA ligase and DNase levels. In the present work we have measured the levels of the DNA polymerases-alpha and -beta in phytohemagglutinin-stimulated lymphocytes during a 12-day period; both enzymes are present at detectable levels at time zero; in correspondence to the peak of DNA synthesis rate (between the fourth and fifth day) a peak of DNA polymerase-alpha is observed, increasing by a factor of approximately 20-fold over the zero time value; subsequently, the level of DNA polymerase-alpha decreases in parallel with DNA synthesis rate. The DNA polymerase-beta is also increased in correspondence to the peak in DNA synthesis rate, but reaches its maximum at later times, between the eighth and tenth day of incubation. The capacity of stimulated lymphocytes to perform repair synthesis following UV damage was measured in the same cells used for the enzyme activity determinations; this capacity also shows two maxima: a first one correlated with the peak in DNA replication rate, and a second one correlated with the peak of DNA polymerase-beta. These data suggest a certain tendency to the specialization of functions in human cell DNA polymerases; the alpha-enzyme seems mainly correlated with DNA replication, whereas the beta-enzyme seems more correlated with the ability of the cell to perform repair type synthesis.

DNA Nucleotidyltransferases↗
PubMed1976

Properties of DNA ligase from uninfected and virus-infected HeLa cells.

HeLa cells contain a high M.W. form of DNA ligase which can be completely converted to a low M.W. form. Stokes radius, frictional ratio, sedimentation coefficient, molecular weight, pH dependence, and heat inactivation rate of the two forms have been studied. The major properties of the two forms of DNA ligase in HeLa cells (in particular molecular weights and pH dependence) resemble those of the "dimer" and "monomer" structures described in cultured human cells (Pedrali, G., Spadari, S., Ciarrocchi, G., Pedrini, M., Falaschi, A. (1973) Eur. J. Biochem., 39 343) . In synchronized HeLa cells, the DNA ligase shows a two fold increase during S phase and parallels the increase in the DNA synthesis rate. DNA ligase increases in parallel with viral DNA synthesis after infection of HeLa cells with vaccinia and Herpes virus but its cofactor requirements and physical properties (including the dimer leads to monomer conversion) are unchanged, suggesting that the newly formed ligase is not virus-coded.

HeLa Cells↗
PubMed1975

RNA-primed DNA synthesis: specific catalysis by HeLa cell DNA polymerase alpha.

We have analyzed and compared the responses of the three major HeLa cell DNA polymerases (alpha, beta, and gamma) to a HeLa DNA template with short RNA or DNA primers hybridized to it. Only DNA polymerase alpha is able to synthesize DNA covalently bonded to the RNA primer via a 3' yields 5' phosphodiester bond. 32P transfer experiments showed that all combinations of ribo- and deoxyribonucleotides are represented in the RNA-DNA linkages but their distribution is nonrandom. The RNA-DNA linked molecules base-paired to a HeLa DNA template strand represent a possible "natural" in vitro primer-template for DNA polymerases and can be extended by all three DNA polymerases (alpha, beta, and gamma). These findings indicate that DNA polymerases beta and gamma are capable of DNA-primed but not RNA-PRIMED DNA synthesis, while DNA polymerase alpha is capable of both RNA-primed and DAN-primed DNA synthesis.

Base Sequence↗
PubMed1974

Levels of some enzymes acting on DNA in xeroderma pigmentosum.

We have determined the levels of DNA polymerase, DNA ligase, a DNase acting on single-stranded DNA, an endonuclease making single-strand breaks in double - stranded DNA and polynucleotide kinase in fibroblasts obtained from nine normal persons and from nine patients with Xeroderma Pigmentosum; the pathological lines belong to the different described clinical forms and to the three different complementation groups described so far. All the enzymes are present in the normal lines and in the Xeroderma lines. The levels are quite variable, but the values obtained in the pathological lines lie within the ones observed in the normal population.

Adolescent↗