Nucleosome stability histone tail domains

Mg (but not Na" ") results in a structure that is equivalent to the 30-nm compact fiber in the extent of condensation [49]. Finally, the independent and critical function of core histone N-termini in chromatin condensation was demonstrated by showing that nucleosomal filaments reconstituted from core histones lacking their N-terminal domains are unable to condense into folded structures upon an increase of Mg " ", despite the presence of properly bound histone H5 ([50,51], see also Ref. [52] for the discussion of the special role of H3 and H4 tails). Thus, the presence of HI is not a sine-qua-non condition for salt-induced chromatin folding, which can proceed in Hi s absence and is an intrinsic property of filaments consisting of spaced core particles. A key question is how many of the features of the native 30-nm compact fiber are due to the presence of histone HI From the available data it seems that HI may influence the intrinsic folding pathway of the chromatin filament by stabilizing a single ordered conformation. This property can have much to do with the cooperativity of HI interactions within chromatin but also with the way HI is bound to the nucleosome and with the efifect it exerts on the path of linker DNA. 

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