Abstract
P816 cells (mouse mastocytes) were labelled with [ 3H]thymidine and [ 14C]lysine during several generations' growth, and during subsequent growth in unlabelled medium chromatin was isolated quantitatively and the ratio ( 14C in histones/ 3H in DNA) was measured. This ratio showed no detectable decrease for over eight generations, indicating that no irreversible dissociation of the major histone fractions from chromatin occurs during growth and mitosis. It was estimated that any minor histone fractions which may show undetectable turnover could not constitute more than 5% of the total histone. When HeLa cells thus labelled were isolated in mitosis after transfer to unlabelled medium, the ratio ( 14C in histones/ 3H in DNA) in their chromatin remained the same as that in the chromatin of interphase cells before transfer. Further, no differences could be detected in the quantitative ratio of histone to DNA, or in the relative amounts of individual histone subfractions (separated by polyacrylamide gel electrophoresis) between the chromatin of cells in interphase and in mitosis. Chromosome condensation at mitosis thus appears to occur without detectable changes in the quantity or types of histones associated with DNA. There was, however, a higher proportion of labelled non-histone protein in the chromatin of mitotic cells.
Published Version
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