Electrophoretic mobility of PM2 DNA treated with ultimate chemical carcinogens or with ultraviolet light

Abstract

Superhelical DNA of the Pseudomonas phage PM2 was irradiated with UV-light or reacted with covalently binding carcinogens, such as 7-bromomethyl-benz[a]anthracene, (Ac)2ONFln, K-region epoxides, and alkylating agents. Migration velocity of the DNA products was determined using agarose gel electrophoresis. In gels of more than 1.3%-1.9% agarose, modified PM2 DNA exhibited a dose-(concentration-)dependent decrease of migration velocity. This phenomenon is probably due to a decrease in superhelix density which caused the compact DNA coil to assume eventually an open-circular conformation. Comparison of the extent of DNA modification with the decrease of migration velocity revealed that the superhelical structure sensitively reflected the chemical DNA alterations. DNA species exhibiting, in 1.6% agarose gels, a migration velocity of up to 30% of that of control DNA showed an increase of velocity in 0.4% agarose. Therefore, in 1.3%-1.9% agarose gels, the decrease os superhelix density is accompanied by an increase of the frictional coefficient, whereas in 0.4%-0.9% agarose gels the same decrease of superhelix density apparently led to a higher degree of flexibility of the macromolecule and/or exposure of additional electric charges.

Bistranded Oxidized Purine Damage Clusters: Induced in DNA by Long-Wavelength Ultraviolet (290−400 nm) Radiation?

“…Figure 1 shows a representative agarose gel containing pUC18 DNA exposed to 0-3.9 MJ/m 2 of UV radiation. The gel clearly shows that the supercoiled molecules (SC) disappear, while the level (36)(37)(38)(39). Figure 1B shows quantitative data from gels such as that shown in Figure 1A.…”

“…The linear population could result from the production of a double-strand break in the circular molecule, either by simultaneous scission of both strands at sites sufficiently close to produce a double-strand break (SC to LIN or REL to LIN) or by sequential production of two single-strand breaks, with the induction of the second strand break near a pre-existing break in the relaxed DNA converting it to a linear molecule. The alterations in mobility at a high UV dose result from modification of the DNA tertiary structure, including unwinding of supercoils due to pyrimidine dimer formation ( − ). Figure B shows quantitative data from gels such as that shown in Figure A.…”