Effect of different sizes of polyacrylic acid on the structure and DNA template properties of isolated rat liver nuclei and soluble chromatin

1. 1. Polyacrylic acid is capable of releasing the DNA template restrictions on isolated rat liver nuclei or soluble chromatin when assayed with either DNA polymerase or RNA polymerase from Escherichia coli B. 2. 2. The ability of polyacrylic acids to release these template restrictions is dependent on their size. Polyacrylic acids of molecular weight 20 400 and 4680 were very effective; whereas polyacrylic acid with a molecular weight of 1260 was completely ineffective. 3. 3. The similarity of the effect of polyacrylic acid in releasing the template restrictions in both isolated nuclei and soluble chromatin indicates that this characteristic is not determined by the ability of the polymer to pass through the nuclear membrane. 4. 4. All sizes of polyacrylic acid were able to precipitate purified unfractionated calf thymus histones; however, the smallest polymer was nearly twice as effective as the larger ones (60 μg histone precipitated by 100 μg polyacrylic acid, mol. wt = 1260). 5. 5. The larger sizes of polyacrylic acid, but not the smallest size, caused an increase in nuclear volume and an optical clearing of isolated nuclei when examined at 600 nm. This phenomenon was accompanied by a release of DNA from the nuclei. 6. 6. The two large sizes of polyacrylic acid were able to protect high molecular weight DNA in nuclei from degradation when nuclear suspensions were incubated at 37 °C in the presence of 2.5 mM Mg²⁺. 7. 7. DNA template characteristics of purified, heat-denatured calf thymus DNA could be completely inhibited by the addition of isolated calf thymus histones. The two larger sizes of polyacrylic acid were specifically able to reactivate the DNA template properties of these histone-inhibited DNA preparations.