Metabolically stable non-histone chromosomal proteins in growing maize roots.

DNA and non-histone chromosomal proteins (NHCP) of meristematic cells of maize primary roots were double labelled in vivo with [3H]- or [14C] thymidine and [14C]- or [3H]-tryptophan respectively. The ratio of labelled tryptophan to labelled DNA was followed during the transition of the meristematic cells of the root tip into the distal zones of finally differentiated cells. It was found that only 20% of the newly synthesized NHCP in the proliferating cells were turned over, while the rest were preserved and found as metabolically stable proteins in the zone of final differentiation. This result is consistent with the hypothesis that some NHCP remain permanently associated with chromatin of non-dividing differentiated cells in order to maintain the genomic characteristics of a given cellular type.