Damage in DNA irradiated with 1.2 MHz ultrasound and its effect on template activity of DNA for RNA synthesis.

When aqueous DNA solution was irradiated with 1.2 MHz continuous ultrasound in the presence of cysteamine, the number of ultrasound-induced double-strand breaks of DNA was not influenced, but the number of ultrasound-induced single-strand breaks of DNA was reduced to about one-fifth that of the irradiated control. When the effect of cysteamine on the template activity of the ultrasound-irradiated DNA was investigated, the cysteamine was found to exert a leveling effect on the linear decrease of the template activity against ultrasonic intensity. Since cysteamine was known as an effective radical scavenger, the results of the experiment were regarded to suggest that (1) the double-strand breaks were exclusively induced by the mechanical effect of ultrasound, (2) the majority of single-strand breaks were produced by water radicals arising from cavitation, (3) the initial part in the decrease of the template activity was due to the double-strand breaks arising from mechanical effect, and (4) the further decrease of the template activity depended mainly on the single-strand breaks arising from water radicals.