Dn. Nikogosyan et al., PHOTOCHEMICAL ALTERATIONS IN DNA REVEALED BY DNA-BASED LIQUID-CRYSTALS, Photochemistry and photobiology, 59(3), 1994, pp. 269-276
The preparations of chicken erythrocyte linear double-stranded DNA and
superhelical plasmid pBR322 DNA were irradiated by continuous low-int
ensity UV radiation (I = 25-50 W/m(2), lambda = 254 nm) as well as by
high-intensity picosecond laser UV radiation (I = 10(11)-10(13) W/m(2)
, 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 character
istic for cholesteric liquid crystal we managed to detect the presence
of photochemical alterations in DNA irradiated by low-intensity UV ra
diation at an absorbed energy of more than 20 quanta per nucleotide. I
n the case of superhelical DNA using enzyme treatment of liquid-crysta
lline dispersions and monitoring the appearance of abnormal optical ac
tivity, we detected the presence of photochemical alterations in DNA m
olecules after low-intensity UV irradiation at an absorbed energy of l
ess than 4 quanta per nucleotide. Under the latter approach using pico
second UV laser irradiation at three different light intensities we we
re able to distinguish the different mechanisms of fine alterations in
DNA secondary structure at an absorbed energy value of about 3 quanta
per nucleotide.