Effects of spermidine and spermine on DNA synthesis in isolated nuclei and on the activity of DNA polymerases alpha and beta from the mammary gland of pregnant rabbit.

The rate of [3H]dTMP incorporation by nuclei isolated from the pregnant rabbit mammary gland was affected by polyamines in two distinct ways: a) a general inhibitory effect was evident when spermidine or spermine were added to the incubation mixture at concentrations 10(-3) - 10(-2) M and 10(-4) - 10(-2) M, respectively; and b) a very specific stimulatory effect of either polyamine at a lower concentration which was observed only when the nuclei were incubated in the presence of horse serum. Furthermore, it was demonstrated that 10(-2) M spermine inhibited the activity of the solubilized nuclear DNA polymerases alpha and beta from the mammary gland of pregnant rabbit, separated by sucrose-density-gradient centrifugation and assayed with activated DNA as a template-primer, while spermidine had no effect at any concentration (10(-9) - 10(-2) M tested.