Polyacrylamide gel electrophoresis of the H1 group of histones extracted from different rat and mouse tissues shows a different pattern of fractions (HI, H1°, H1° met) when the two species are compared. Different tissues of each species also have a different pattern of HI histone fraction and subfraction. However, the age-associated changes of mouse HI histones from liver and spleen chromatin show the same type of alteration of fraction ratios which had been demonstrated in our earlier research with rat tissues. In both species there is a relative increase of the F1° and F1° met fractions in tissues from old animals. The presence of the F1° fraction in only non-dividing cells suggests that there may be an age-specific type of chromatin condensation.
The non-histone chromatin (NHC) proteins which are loosely bound to DNA were extracted from young and old mouse and rat liver chromatin by 0.35 M NaCl and fractionated into three groups: water-soluble, 0.14 M NaCl soluble and 0.35 M NaCl soluble. NHC proteins in each fraction were separated by SDS-disc polyacrylamide gel electrophoresis. Special attempts were made to locate minor high-molecular-weight proteins which develop faint bands. It was found that the ageing of liver cells is associated with increase in number and quantities of high-molecular-weight NHC proteins in the water-soluble group. Salt-soluble groups of NHC proteins show fewer changes of pattern.
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