LINKER DNA BENDING INDUCED BY THE CORE HISTONES OF CHROMATIN

We have previously reported that ionic conditions that stabilize the folding of long chromatin into 30-nm filaments cause linker DNA to bend, bringing the two nucleosomes of a dinucleosome into contact [Yao, J., Lowary, P. T., & Widom, J. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 7603-7607]. Dinucleosomes are studied because they allow the unambiguous detection of linker DNA bending through measurement of their nucleosome-nucleosome distance. Because of the large resistance of DNA to bending, the observed compaction must be facilitated by the histones. We have now tested the role of histone H-1 (and its variant, H-5) in this process. We find that dinucleosomes from which the H-1 and H-5 have been removed are able to compact to the same extent as native dinucleosomes; the transition is shifted to higher salt concentrations. We conclude that histone H-1 is not essential for compacting the chromatin filament. However, H-1 contributes to the free energy of compaction, and so it may select a single, ordered, compact state (the 30-nm filament, in long chromatin) from a family of compact states which are possible in its absence.