[Study of DNA synthesis stimulators in nerve tissue cells]

Ontogenetic changes in DNA synthesis in different divisions and regions of the brain occur via different mechanisms, which is conditioned by changes in the composition and properties of corresponding mediators. Tissue extracts obtained from the parts of brain characterized by intensive cell division (cortex of 15-17-day-old embryos or cerebellum of 8-10-day-old animals) can stimulate the incorporation of labeled precursors into brain cell DNA in both neonatal and adult rats. Using desalting at increasing concentrations of ammonium sulfate, gel filtration on sephadexes and isoelectrofocusing, three fractions of DNA synthesis stimulators whose isoelectric points lie at acidic, neutral and alkaline regions of pH, were isolated. A method is described, which can be employed for isolation in a pure state and determination of some physico-chemical properties of an acid activator. The latter is a low molecular weight peptide causing marked stimulation of [3H]thymidine incorporation into nervous tissue cell DNA in an in vitro system, when taken at a concentration of about 1 microgram/ml.