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Ultracentrifuge tudies of histone fractions from calf thymus deoxyribonucleoprotein.

ABSTRACT: Molecular weights and sedimentation coefficients of four major fractions of calf thymus histones were measured. The minimum molecular weights were determined in concentrated solutions of guanidine hydrochloride. The results indicate that, with the possible exception of fraction F3, the fractions are heterogeneous. Comparisons in 0.1m-sodium chloride suggest that fraction F1 does not aggregate and show that fractions F2(a) and F3 aggregate to form larger complexes than does fraction F2(b). The degree of aggregation of each fraction is independent of pH in the range pH1-7. Detailed studies with fraction F2(b) have confirmed that the change in sedimentation coefficient observed as the sodium chloride concentration of the solution is increased results from increases in the apparent molecular weight of the sedimenting units. It has been found that the molecules of fraction F2(b) are present as single molecules only in sodium chloride solutions of 33mm or less. At these low concentrations the effects of charge greatly increase the concentration dependence of the sedimentation rate; the results can, however, be interpreted by using the theory developed by Alexandrowicz & Daniel (1963) and Daniel & Alexandrowicz (1963).

SUBMITTER: Ewars PA

PROVIDER: S-EPMC1184847 | biostudies-other | 1969 Sep

REPOSITORIES: biostudies-other

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Project description:1. The interactions of histone fractions with 8-anilinonaphthalene-1-sulphonic acid were investigated by fluorimetry and spectrofluorimetry and the results were interpreted with the aid of equilibrium-dialysis techniques. 2. Characteristic differences were found between the various histone fractions, and with fractions F3 and F2a the binding was found to be salt-dependent. 3. Evidence was obtained indicating a slow change of the physical state of fractions F3 and F2a in the presence of salt, and the binding by these two fractions in the presence of salt was greater by an order of magnitude than by fractions F1 and F2b. 4. Conditions favouring binding were also those favouring histone aggregation; SO(4) (2-) ions activated binding at a lower concentration than Cl(-) ions; urea, guanidinium ions and high concentrations of I(-) ions were inhibitory to binding. 5. After histones had been kept in the presence of salt for a long time the reversal of interaction on decreasing the salt concentration was incomplete. 6. The inhibition of binding by fraction F2a in the presence of urea or fraction F2b depended on the time sequence of addition of the reagents. 7. Artificial nucleoproteins made by precipitating DNA with the histone fractions in neutral 0.14m-sodium chloride showed the same order of interaction as was found for the fractions in solution. 8. Comparison of the binding by fraction F2a with that by bovine plasma albumin showed that in both cases there were a large number of weakly binding sites but that fraction F2a lacked the small number of strongly binding sites found in albumin. No slow change of binding in the presence of salt was found for albumin. 9. Binding by fraction F2b increased the affinity of the protein for further molecules of the adsorbate. 10. The results are discussed in relation to the close relationship between binding and aggregation and the possible role of non-polar interactions as determined by the balance between polar and non-polar amino acids in the histone fractions.

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Ultracentrifuge tudies of histone fractions from calf thymus deoxyribonucleoprotein.

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