The ultraviolet (UV)-induced formation of cyclobutyl pyrimidine dimers in Escherichia coli deoxyribonucleic acid (DNA) in vitro has been investigated in terms of the mechanism of inhibition by acridine dyes, the effect on dimer yield of specific singlet and triplet quenchers, and the mechanism of dimer formation. Our results indicate that (a) energy transfer is important in dimer reduction by acridines, (b) this transfer occurs from the singlet (S(1)) of DNA, and (c) at room temperature triplet quenchers do not reduce dimer yield in DNA.

Acetone↗

PubMed1969

Inhibition of pyrimidine dimer formation in DNA by cationic molecules: role of energy transfer.

In addition to the acridine dyes, acridine orange and proflavine, we find that three other cationic molecules which bind to DNA-ethidium bromide, chloroquine, and methyl green-inhibit the production of cyclobutyl pyrimidine dimers by ultraviolet radiation. Intercalation is not necessary for dimer inhibition. The long range nature of the inhibition implies that energy transfer is responsible. The transfer is between the lowest excited singlet state of DNA and the acceptor singlet, and seems to involve the Förster mechanism.

Acridines↗

PubMed1969

Probes of DNA structure and interactions. Effects of copper II on ultraviolet-induced pyrimidine dimer formation.

Cu(II) affects the yield of cyclobutyl dimers induced in DNA by 254 nm radiation. The effects are a function of r, the ratio of Cu(II) to DNA phosphate, and of the ultraviolet (UV) fluence; they seem to reflect two types of copper complexes with DNA. The first probably involves "exterior" binding to the bases of native DNA and increases [unk]TT formation (without affecting [unk]UT yield) by raising the energy levels of bases other than thymine. The second seems to occur only at high ratios (rs) and only after the structure has been opened locally by UV radiation; it involves "interior" binding of Cu(II) to the bases. This complex tends to decrease dimer yield by holding the bases apart and/or by lowering the energy levels of bases other than thymine. These results illustrate the potential use of DNA photoproducts and ligands to probe the structure and interactions of DNA in vitro and perhaps also in vivo.

Carbon Isotopes↗

PubMed1968

Cancer in a mission hospital in South Africa. With emphasis on cancer of the cervix uteri, liver and urinary bladder.

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Black People↗

PubMedDate not supplied

Separation of chromosomal length DNA molecules: pneumatic apparatus for rotating gels during electrophoresis.

The maximum length of DNA molecules that can be separated by gel electrophoresis can be increased greatly by periodically altering the direction of the electric field with respect to the gel by an angle that exceeds 90 degrees. One method involves rotating the gel by the desired angle in alternate directions periodically during electrophoresis. We describe a modification of the rotating gel electrophoresis apparatus developed by Serwer (Electrophoresis 1987, 8, 301-304) that uses a pneumatic rotary actuator instead of a stepping motor, hence reducing the cost by about 50%. Other advantages of our design are a lower center of gravity that makes the apparatus more stable and the removal of all electrical power from beneath the fluid-filled electrophoresis chamber. We present data demonstrating the separation of chromosomal length DNA molecules from Saccharomyces cerevisiae strain 334 into 14 resolved bands in parallel lanes.

Costs and Cost Analysis↗

PubMedDate not supplied

Gel electrophoresis method for quantitation of gamma ray induced single- and double-strand breaks in DNA irradiated in vitro.

We describe a method based on gel electrophoresis for the quantitation of strand breaks in DNA and demonstrate its application to the measurement of single- and double-strand breaks formed by gamma-rays for DNA irradiated in vitro. For single-strand breaks, our data span the dose range from 0.1 to 1 Gy, while for double-strand breaks doses were from 3 to 15 Gy. In agreement with results obtained using other techniques, we find that the dose response function for single-strand breaks is linear while the dose response function for double-strand breaks is curved, indicating that it is the sum of both linear and quadratic components. We discuss factors that determine the sensitivity of the method and indicate approaches to make possible the quantitation of strand breaks in the DNA of cells irradiated with sublethal doses.

DNA↗