The histone core exerts a dominant constraint on the structure of DNA in a nucleosome. |
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Authors: | J J Hayes J Bashkin T D Tullius A P Wolffe |
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Institution: | Laboratory of Molecular Embryology, National Institute of Child Health and Human Development, Bethesda, Maryland 20892. |
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Abstract: | We have examined the structures of unique sequence, A/T-rich DNAs that are predicted to be relatively rigid oligo(dA).oligo(dT)], flexible oligod(A-T)]], and curved, using the hydroxyl radical as a cleavage reagent. A 50-base-pair segment containing each of these distinct DNA sequences was placed adjacent to the T7 RNA polymerase promoter, a sequence that will strongly position nucleosomes. The final length of the DNA fragments was 142 bp, enough DNA to assemble a single nucleosome. Cleavage of DNA in solution, while bound to a calcium phosphate crystal, and after incorporation into a nucleosome is examined. We find that the distinct A/T-rich DNAs have very different structural features in solution and helical periodicities when bound to a calcium phosphate. In contrast, the organization of the different DNA sequences when associated with a histone octamer is very similar. We conclude that the histone core exerts a dominant constraint on the structure of DNA in a nucleosome and that inclusion of these various unique sequences has only a very small effect on overall nucleosome stability and structure. |
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