Metabolic Behaviour of Nonhistone Chromosomal Proteins in Proliferating and in Resting Fibroblasts

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Abstract
The metabolism of nonhistone chromosomal proteins was studied in 2 lines of cells showing a different degree of contact inhibition: human [lung] diploid fibroblasts, which are easily contact-inhibited and Chinese hamster [BIIdii, FAF-28] fibroblasts, which were made to stop proliferating by fasting. By following the 3H/14C ratio of [3H]tryptophan-labeled nonhistone chromosomal proteins and [14C]thymidine-labeled DNA in chase experiments 3 main groups of these proteins could be detected with respect to their metabolic behavior: a metabolically stable group which was acid-insoluble and represented the bulk of nonhistone chromosomal proteins in proliferating cells; this group was conserved when the cells enter a resting phase; a metabolically labile group which was acid-soluble and was observed as a minor fraction in proliferating cells; a metabolically labile group which was acid-insoluble and accumulated in resting cells; this fraction was much larger in contact-inhibited cells. Stimulation of cell proliferation by trypsinization decreased the amount of nonhistone chromosomal proteins in resting cells to the basic level observed in proliferating cells.