DNA synthesis in isolated nuclei from the brains of rats at different post-partal stages and the infant rat brain cytosol factor stimulating the DNA synthesis in infant rat brain nuclei

Abstract

[ 3H]TTP incorporation into DNA of isolated nuclei from the brains of rats at different post-partal stages, as well as the effects of the adult and the infant rat brain cytosols upon the DNA synthesis in the isolated nuclear system, have been investigated. The nuclear system requires the four deoxyribonucleoside triphosphates, ATP and Mg 2+ for a maximum activity and DNA synthesis proceeds linearly within 30 min of incubation. A large portion of [ 3H]TTP incorporated into DNA is sensitive to actinomycin D inhibition and seems to be DNA polymerase dependent, while the remaining incorporation (approx. 20 % in the infant nuclear system and approx. 40 % in the adult nuclear system) is less sensitive to actinomycin D inhibition, proceeds without dATP, dCTP and dGTP and seems to be due to the terminal DNA nucleotidyltransferase activity. The nuclear activity of [ 3H]TTP incorporation into DNA increases after birth, reaches a maximum on the fifth day and then declines rapidly, reaching the adult level ( i. e. one half the maximum level) on the 22nd day after birth. [ 3H]TTP incorporation into DNA of isolated infant rat brain nuclei is stimulated specifically by the infant rat brain cytosol. The active principle in the infant rat brain cytosol seems to be thermostable and low molecular, and differs from the stimulatory factor present in the serum.