The process of transcription in thymus cells of X-irradiated rats. Report 3. Template activity and some structural characteristics of the chromation

The template activity of the thymus chromatin increases 30 min after total-body irradiation of rats with a dose of 400 rad. After 2 and 4 hours it decreases. Irradiation delays the mitosis of thymocytes in culture under the action of phytohemagglutinin immediately after exposure. The effect grows with time. The ability of chromatin to bind phytohemagglutinin is suppressed 30 min after irradiation which is followed, after 2 and 4 hours, by activation of complex formation. Irradiation does not influence the fractional composition of histones of a ''residual'' chromatin but gives rise to an additional fraction in the composition of histones of PDN