The native, denatured and renatured states of deoxyribonucleic acid

Influence of molecular weight of DNA on the determination of anti-DNA antibodies in systemic lupus erythematosus (SLE) sera by radioimmunoassay

Using a radioimmunoassay (RIA) based on the Farr technique with radioactively labeled 3-H-DNA for quantitative measurements of anti-DNA antibodies in sera of patients with systemic lupus erythematosus (SLE), the influence of molecular weight of DNA (ranging from 0.1 times 10-6 to 22.0 times 10-6 daltons) on binding and precipitation in this system has been investigated. Comparing our results with mathematical models it follows that one antibody molecule is fixed on the average to a statistical DNA segment of 2 times 10-6 to 4 times 10-6 daltons. Furthermore binding capacity of the DNA was found to be independent of the molecular weight, as demonstrated in a double label experiment using 14-C and 3-H-labeled DNA of different size. However, the amount of radioactivity precipitated was found to depend on the molecular weight of the labeled DNA following a non-linear function. It was calculated that a minimal ratio of fixed antibody molecules per a certain size of DNA was necessary for precipitation. The mathematical treatment of the observed non-linear precipitation dependence will be discussed using various statistical models. Our results indicate that the quantitative measurements of anti-DNA antibodies with the Farr technique e.g. for diagnosis and control of SLE in clinical immunology is highly dependent on the molecular weight of the labeled DNA used in the assay system and reliable results are only obtained with DNA of a sufficiently high molecular weight.

Absence of mutation following ultrasonic treatment of Bacillus subtilis cells and transforming deoxyribonucleic acid

Possible mutagenic effects of ultrasound at medical dosages have been assessed using genetic systems of Bacillus subtilis. The induction of mutations, after treatment of cells and of extracted transforming DNA with ultrasound has been tested. High-frequency (2 MHz diagnostic regime and higher intensities) ultrasound was unable to increase significantly the spontaneous frequency of back-mutation of an auxotrophic strain. Moreover, high-frequency treatments (1.5 MHz diagnostic and therapeutic regimes) were incapable of producing detectable levels of mutagenic lesions after in vitro irradiation of transforming DNA. Slight decreases in transforming activity of the treated DNA were apparent while the degree of linkage between two contiguous markers was unaffected. It is concluded that the ultrasound treatments employed under the conditions pertaining do not result in production of detectable mutagenic effects in cells or in vitro treated DNA. Before extrapolating such results to the human hazard situation, it is suggested that tests using genetic systems of higher organisms should be carried out.

Interaction of steroids with nucleic acids

17beta-Estradiol and testosterone bind to both native and denatured DNA, and to RNA and poly(A)-poly(U). Binding affinity depends on the conformation of nucleic acid. Lowering the electrolyte concentration and raising the temperature increase the binding of 17beta-estradiol to native DNA and decrease that to denatured DNA. In 0.01 M NaCl and at 37 degrees, more 17beta-estradiol is bound to native DNA than to denatured DNA. Higher binding of steroid to denatured DNA relative to native DNA at low temperature and high ionic strength is related to larger fraction of binding sites per unit nucleotide in denatured DNA. In addition to 17beta-estradiol and testosterone, 17alpha-estradiol, 17beta-estradiol-3-methyl ether and 19-nortestosterone also stabilize the structure of nucleic acids and poly(A)-poly(U) against thermal denaturation. The 17beta-estradiol induced elevation of the T-m of DNA is diminished by methanol or high NaCl concentration. These results indicate the involvement of hydrogen bonding and hydrophobic interactions between steroids and nucleic acids. The results of binding isotherms and optical studies suggest a conformational dependence of the binding of steroids to nucleic acids.

Intermolecular linking and fragmentation of DNA by beta-propiolactone, a monoalkylating carcinogen

Brief exposure to beta-propiolactone (BPL) increases the sedimentation rate of purified Escherichia coli DNA in neutral and alkaline sucrose gradients. However, when electrophoresed in polyacrylamide-agarose gels, this BPL-treated DNA moves ahead of the control. Longer incubation with BPL gives rise to two new fractions, the first one sedimenting as a heterogeneous material of 6-8S, and the second one of very high sedimentation velocity. In acrylamide-agarose gels, the first fraction is again recovered in the 6-8S area, while the second fraction does not enter the gel at all. The DNA at this stage is hyperchromic in ultraviolet light suggesting that as much as 20% may be denaturated. Coliphage lambda DNA treated briefly with BPL and spread in a protein monolayer appears under the electron microscope as a rigid, extended molecule, up to 15% longer than the control DNA, and usually in compact, folded configurations suggesting intramolecular linking. After longer exposure, localized denaturation associated with single-strand breaks is observed. The single-stranded "whiskers" then interact with other DNA molecules, creating highly complex branched networks of single- and multi-stranded DNA. The possible relevance of these observations to the mechanisms involved in carcinogenesis and mutagenesis is considered.

Chromatography of transforming deoxyribonucleic acid on methylated albumin and by gel filtration

1. Native DNA from two strains of Bacillus subtilis was chromatographed by stepwise elution from MAK (methylated albumin on kieselguhr). 2. Transforming activity was confined to two out of the three main fractions, activity being distributed between the two peaks differently for DNA from the different strains. 3. Fractionation of DNA from both strains on 2% agarose gel gave two components. Approx. 75% of the material was eluted within the void volume of the column. Approx. 25% of the material consisted of degradation products of lower molecular weight. 4. Chromatography on MAK of the material of high molecular weight eluted from agarose gel gave a number of peaks differing in molecular weight, indicating that degradation of the DNA takes place during chromatography on MAK. 5. The distribution of transforming activity among the fractions from MAK suggests that degradation occurs preferentially in certain regions of the DNA.