Metabolic stability of nonhistone chromosomal proteins in two different classes of developing rat brain nuclei

The metabolic behaviour of NHCP was studied in rat brain nuclei from fully differetiated cells and in nuclei from still differentiating cells. Eight-day-old rats were injected intracisternally with [14C]thymidine and [3H]tryptophan and the 3H/14C ratio of the chromatin was followed for a period of 33 days. It was found that in the fraction of differentiated cells this ratio remained unchanged, showing the presence of metabolically stable NHCP. At the same time in the fraction containing nondifferentiated cells a substantial part of the NHCP was turned over, which was indicated by a sharp decrease in their 3H/14C ratio with time.