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L F CAVALIERI

Publications and source records attributed to L F CAVALIERI.

17 recordsLinked to original sources
PubMed1962

The renaturation of denatured DNA.

The kinetics of renaturation of heat-denatured DNA from E. coli and pneumococcus have been examined by ultraviolet absorption measurements. The molecularity of the reaction was assessed by three independent treatments of the data, and all lead to the conclusion that renaturation is essentially first order at 60 degrees ; at 70 degrees and 80 degrees there is an increasing second order component, resulting in simultaneous unimolecular and bimolecular kinetics. The unimolecular kinetics rule out reaction between two, kinetically separate strands, indicating rather the zippering-up of a single, denatured entity. The bimolecular kinetics can be attributed to the complexing of two such entities; thus, the genetic or density-labeled complexes that have been observed by other investigators can be accounted for without invoking strand separation. Since renaturation at best is never complete, the free ends of two renatured molecules permit sufficient bimolecular reaction to produce density hybrids. The observed kinetics can be accounted for if the hydrogen bonds of DNA are broken during heat denaturation but the strands do not separate. Light scattering supports this by showing that the molecular weight is unchanged by denaturation. Since there is no existing evidence that is inconsistent with this hypothesis, it is reasonable to conclude that heat denaturation does not completely separate the entangled strands of the DNA molecule.

DNA↗
PubMed1961

The replication of DNA I. Two molecular classes of DNA.

Two classes of DNA have been distinguished on the basis of their reaction to heating in cesium chloride. DNA from proliferating sources is cleaved in half by such treatment, whereas DNA from non-proliferating sources is unaffected in molecular weight. This has been shown by two independent techniques. The relationship between the molecular units produced by cesium chloride treatment and the units conserved during DNA replication is discussed.

DNA↗
PubMed1961

The replication of DNA II. The number of polynucleotide strands in the conserved unit of DNA.

The kinetics of degradation of DNA by deoxyribonuclease II have been studied, using the techniques of light scattering, viscosity, and titration. Theoretical equations have been derived for both random and non-random attacks, and all assumptions have been evaluated. It has been shown that these equations permit a valid calculation of the number of polynucleotide strands per molecule. The results have been verified by two independent experimental methods. DNA from proliferating sources was found to be four-stranded; DNA from non-proliferating sources was found to be two-stranded. The implications of these findings are discussed.

DNA↗
PubMed1961

The replication of DNA III. Changes in the number of strands in E. coli DNA during its replication cycle.

DNA has been isolated from synchronized cultures of E. coli 15(T)- at various times. At first the DNA was four-stranded (and indistinguishable in all respects from log phase E. coli DNA), but at the start of DNA synthesis the DNA was found to have halved its molecular weight and to have become two-stranded. This sample had all the properties of undenatured, double-helical DNA, and behaved in all respects like DNA from non-proliferating sources. The replication cycle of the DNA molecule has thus been shown to consist of an alternation between the four- and two-stranded forms, the latter being the conserved unit. The evidence provided by the three papers of this series with respect to DNA and chromosomal structure and replication is discussed and summarized.

DNA↗
PubMed1961

Four-stranded DNA as determined by electron microscopy.

Pneumococcus DNA, of weight-average molecular weight 1.6 million by light scattering, had a weight-average length of 4300 A by electron microscopy. Thus, the average mass per unit length was 370 molecular-weight units per A, or approximately two times that expected (208) for a Watson-Crick double helix. This corresponds to an average of 3.6 strands per molecule, which is close to that obtained by other methods. Morphologically, all the particles in the micrographs were relatively stiff, and had a cross-sectional height of 20 to 30 A. Some divided into two stiff branches of the same height, apparently double helical. Where the branches combined into one (minimally four-stranded) structure they apparently lay side by side in close association.

Cross-Sectional Studies↗