Photochemical alterations in DNA revealed by DNA-based liquid crystals.

The preparations of chicken erythrocyte linear double-stranded DNA and superhelical plasmid pBR322 DNA were irradiated by continuous low-intensity UV radiation (I = 25-50 W/m2, lambda = 254 nm) as well as by high-intensity picosecond laser UV radiation (I = 10(11)-10(13) W/m2, lambda = 266 nm). The effect of DNA secondary structure alterations on the formation of liquid-crystalline dispersions from UV-irradiated DNA preparations was studied. It was shown that in the case of linear DNA, watching the disappearance of abnormal optical activity characteristic for cholesteric liquid crystal we managed to detect the presence of photochemical alterations in DNA irradiated by low-intensity UV radiation at an absorbed energy of more than 20 quanta per nucleotide.

Method for the introduction of the reactive functional groups via cytidine residues and/or 3'-terminal of the nucleic acids.

A number of polyfunctional O-substituted hydroxylamines H2NO-R-X (X = SH; -NH2; -P(O) (OH)2; -COOH; etc.) were constructed and synthesized as a mean for the administration of the reactive functions through cytidines or into 3 -oxidised terminal of nucleic acids.

Footprinting of DNA secondary structure by high-intensity (laser) ultraviolet irradiation.

The action of high-intensity ultraviolet pulse laser radiation on a 161 bp fragment of pBR 322 DNA (EcoRI-MspI fragment) was studied. At doses up to 5 X 10(18) photons/cm2 the N-glycosidic bond splitting is negligible. The action of hot piperidine on irradiated DNA leads to chain splitting at the residues, modified via biphotonic processes.