| Abstract: | The rate of 14C]NAD incorporation into chicken liver nuclear histones was studied under conditions of DNA damage by N-methyl-N-nitrosourea and pancreatic DNAase I. With an increase in N-methyl-N-nitrosourea concentration from 8.5 X 10(-2) to 34.0 X 10(-2) mM, the ADP ribosylation of histones increases by 20% as compared to the control. In DNAase I-treated nuclei, the binding by histones of 14C]NAD sharply increases, reaching its maximum (18.3 X 10(-8) mM) at 30% cleavage of DNA. When 50% of DNA was cleaved, the rate of 14C]NAD incorporation into the histones was 8.0 X 10(-8) mM as compared to 6.1 X 10(-8) mM/mg protein in control samples. The poly(ADPR)polymerase activity was increased in both cases. It was shown that the NAD-pyrophosphorylase activity in chicken liver nuclei treated with N-methyl-N-nitrosourea does not differ from the control one, while in DNAase I-treated nuclei the maximum of the NAD-pyrophosphorylase activity was achieved, as well as the maximum of 14]NAD incorporation into the histones within the range of DNA damage of 25-35%, being equal to 37 X 10(-8) mM NAD/min/mg protein as compared to 26.0 X 10(-8) mM/min/mg protein in the control. At different degrees of DNA damage, the average length of the poly-ADP-ribose chain did not practically alter, thus suggesting the increase in the number of polymer binding sites in the histones. |
