The inhibition of nuclear DNA polymerizing activity by captan

A study was conducted concerning the inhibition of calf thymus nuclear DNA synthesis by captan. Captan was shown to be toxic to the in vitro incorporation of ³H]dTTP into calf thymus DNA, with an ID₅₀ value of 0.16 mM being measured. This inhibition was determined to be independent of Mg²⁺ concentration. Although intact nuclear activities were affected, the soluble DNA polymerizing activity isolated from calf thymus nuclei exhibited no inhibition when exposed to captan. Treatment of purified calf thymus DNA with 10^?5 and 10^?4M captan caused an elevation of the T_m by 2 and 6°C, respectively. The inhibitory characteristic of captan on DNA polymerizing activities and the influence of this compound on the thermostability of DNA indicate a mechanism of inhibition which is located in the nucleus and is possibly related to the template function of DNA and/or with the nuclear DNA polymerizing enzymes.