THE EFFECT OF ULTRASONIC IRRADIATION ON THE TEMPLATE ACTIVITY OF CALF THYMUS DNA

An aqueous solution of calf thymus DNA was irradiated with 19.5 kHz ultrasound, and the template activity of the DNA for RNA synthesis in vitro was investigated. The template activity of the DNA was assayed by the incorporation of 14C-AMP into the synthesized RNA. The template activity of DNA decreased rapidly by sonication for the initial short period, and then further decreased exponentially with the increment of sonication period. The neutral sucrose gradient analysis of the sonicated DNA showed that the rapid reduction of the molecular weight was induced for the initial short period of sonication, and that the further sonication had little effect on it. This result indicated that the initial rapid decrease of the template activity was mainly due to the reduction of the molecular weight, i.e., due to the double strand breaks. The production of single strand breaks in the sonicated DNA was also investigated by alkaline sucrose gradient analysis. It was found that the number of single strand breaks increased with the increment of sonication period. The single strand breaks produced by sonication seem to participate in the above mentioned exponential decrease of the template activity. © 1981 Oxford University Press. All rights reserved.