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A study of calf thymus histone fraction F2(b) by gel filtration.

ABSTRACT: The gel-filtration behaviour of calf thymus histone fraction F2(b) was studied at three different salt concentrations (0.01m-, 0.10m- and 1.00m-sodium chloride) and two different pH ranges (pH3-4 and pH6.7-7.1). Other histone fractions [F1, F2(a) and F3] were also utilized to assist interpretation of the data. It was found that the Stokes radius of histone fraction F2(b) was not significantly changed when the salt concentration was increased, implying that the aggregation of the individual histone molecules (Edwards & Shooter, 1969) resulted in only relatively minor changes in the hydrodynamic volume. Aggregation would appear to be due to the salting out of hydrophobic regions giving rise, in the aggregate, to a compact core of hydrophobic groups from which protrude the remaining basic parts of the molecule. Repulsion between charged groups on the basic regions of individual histone molecules would give the aggregate approximately spherical symmetry, the diameter of the aggregate approximating to the length of a single histone molecule.

SUBMITTER: Edwards PA

PROVIDER: S-EPMC1179569 | biostudies-other | 1970 Nov

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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A study of calf thymus histone fraction F2(b) by gel filtration.

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