Turnover of chromosomal proteins from rat liver

Abstract

There is a marked heterogeneity of turnover rates among rat liver chromosomal proteins. The relative rates of degradation of chromosomal proteins were studied by a double isotope technique in which a single injection of [ 14C]leucine was administered 3 days prior to [ 3H]leucine. As indicated by 3H: 14C ratios of chromosomal proteins separated on sodium dodecyl sulfate-acrylamide gels, there is a general correlation between relative degradation rates and molecular size of the protein. Similar results were obtained for total chromosomal proteins and for isolated acidic proteins. The relative degradation rates of chromosomal proteins in vivo correlates with their sensitivity to pronase in vitro if the proteins are first extracted from the chromatin complex. Within the intact chromosome structure, however, there is no relationship between in vivo and in vitro degradation rates. These findings suggest that the inherent sensitivity of chromosomal proteins to proteolytic digestion is one determinant of their in vivo degradation rates, and that chromosomal proteins may be degraded in vivo primarily in a dissociated form.