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Biomedical subjects

S L Marcus

Publications and source records attributed to S L Marcus.

At least 73 records · Page 4Linked to original sources
PubMed1977

The effect of magnesium and manganese ions on the structure and template activity for reverse transcriptase of polyribocytidylate and its 2'-0-methyl derivative.

The secondary structure of the hydrogen bonded hybrids polycytidylate-oligodeoxguanylate (poly(rC)-(dG)12-18 and poly (2'-oMe) cytidylate-oligodeoxyguanylate (poly (rCm)-(dG)12-18 was studied at several magnesium and manganese ion concentrations. These hybrids are effective template-primer complexes for the synthesis of poly(dG) by avian myeloblastosis virus (AMV) DNA polymerase under disparate ionic conditions. Circular dichroism spectra and thermal melting data were obtained as a function of ion concentration, including conditions that allow optimum rates of poly (dG) synthesis by each complex. These studies demonstrate that both hybrids can change conformation and stability depending on their ionic environment. Comparison of enzyme activity and physical data suggest that the polymerase recognizes particular secondary structure features. Changes in the activity of the AMV polymerase can be induced by varying the Mg++ and Mn++ concentrations alone and in combination. These variations in enzyme activity are correlated with observed changes in the base-stacking alignment of the synthetic template primers. The ions, therefore, seem to affect enzyme activity by altering the conformation of the polnucleotide complexes.

Avian Myeloblastosis Virus↗
PubMed1977

Specific inhibition of DNA polymerase-associated RNase H by DNA.

The RNase H activity associated with several RNA-directed DNA polymerases is inhibited by the addition of DNA, in contrast to RNase H activity from enzymes devoid of polymerizing activity. Kinetic investigations of the inhibitory effect of DNA, using purified Rauscher leukemia virus DNA polymerase as a test enzyme, revealed that the addition of DNA to an ongoing RNase H reaction causes an immediate cessation of RNase H activity. Concomitant initiation of DNA synthesis by inhibitory DNA can occur, provided that appropriate substrate and primer is available. Thus, in addition to providing a simple test for the distinction between polymerase-associated and polymerase-independent RNase H activity, this study strongly supports the concepts that (i) RNase H activity expressed by several mammalian oncoviral reverse transcriptases is an integral part of that molecule, and (ii) that the catalytic site of RNase H activity is also involuved in template-primer binding.

DNA↗
PubMed1976

Tubal and uterine motility in vivo in the rhesus monkey.

Previous data indicate that there are definite qualitative and quantitative patterns of tubal activity during the various phases of the menstrual cycle. In the present investigation, the simultaneous activity of the uterus and Fallopian tube was recorded in vivo in mature rhesus monkeys throughout the menstrual cycle. The observations indicate that there are characteristic patterns of both tubal and uterine activity, depending on the various phases of the menstrual cycle. The simultaneous recordings of tubal and uterine activity show that the tubal and uterine contractions are not synchronous or even have a similar pattern. The presence of a transmetrial catheter for recording of uterine activity seems to modify the patterns of tubal activity, particularly during the ovulatory phase. It seems possible that the transmetrial catheter has a similar effect as an intrauterine contraceptive device in this species.

Animals↗
PubMed1976

Observations on template-specific conditions for DNA synthesis by avian myeloblastosis virus DNA polymerase.

The effects of Mg++, Mn++, and KCl addition, individually and in combination, on the rate of DNA- and RNA-primed DNA synthesis by avian myeloblastosis virus DNA polymerase (reverse transcriptase) using a variety of natural and synthetic template-primer combinations were examined. Optimal divalent cation concentrations were found to vary by as much as 10-fold depending upon the template-primer used to direct synthesis. Addition of KCl to reaction mixtures containing optimal divalent cation concentrations produced stimulation or inhibition of DNA synthesis which was also template-specific. DNA synthesis on the modified template poly (2'-0-methylcytidylate) was uniquely stimulated by combinations of divalent cations. With Mg++ as divalent cation, deviations from classical Michaelis-Menten kinetics of substrate saturation were observed with all template-primers tested.

Avian Leukosis Virus↗
PubMed1974

Evidence for allosterism in in vitro DNA synthesis on RNA templates.

Hemoglobin mRNA and (rA)(n).(dT)(10) have been used as primer-templates in a kinetic study of DNA synthesis with Escherichia coli DNA polymerase I (DNA nucleotidyl transferase, EC 2.7.7.7) and Mason-Pfizer monkey virus reverse transcriptase (RNA-directed DNA polymerase). The rate versus enzyme concentration curve is sigmoidal and is consistent with a cooperative phenomenon. The results could be interpreted in terms of the formation of an active complex containing enzyme dimers (or oligomers) on the primer-template. We have also observed sigmoidal kinetics in rate versus deoxynucleotide triphosphate concentration. These results are consistent with an allosteric mechanism in which the triphosphates act as both modifiers and DNA precursors. In the critical range, a 6- to 8-fold increase in both enzyme and triphosphate concentrations can lead to a 1500-fold increase in the rate of synthesis on an RNA template. Thus, small changes in enzyme and precursor concentrations could play a regulatory role in vivo.

Adenosine Triphosphate↗
PubMed1974

Purification of avian myeloblastosis virus DNA polymerase by affinity chromatography on polycytidylate-agarose.

Polycytidylic acid [poly(rC)] covalently linked to cyanogen bromide-activated agarose is an effective affinity matrix for the RNA-dependent DNA polymerase from avian myeloblastosis virus. Poly(rC)-agarose is capable of binding large quantities of avian myeloblastosis DNA polymerase, which is then eluted by using a linear KCl gradient of increasing concentration. The DNA polymerase isolated from crude, detergent-disrupted virions by a single pass through columns of poly(rC)-agarose appears nearly homogeneous (approximately 90% pure) as determined by sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis. Complete recovery of input enzymatic activity was obtained. Results suggest that polyribonucleotide columns may provide a high-yield, rapid method for the purification of oncornaviral DNA polymerase.

Avian Leukosis Virus↗