Linker histone protects linker DNA on only one side of the core particle and in a sequence-dependent manner

The protection against micrococcal nuclease digestion afforded to chromatosomal DNA by the presence of a linker histone (H1 degrees) has been quantitatively measured in two reconstituted systems. We have used chromatosomes reconstituted at two distinct positions on a DNA fragment containing the 5S rRNA gene from Lytechinus variegatus and at a specific position on a sequence containing Ga14- and USF-binding sites, In all cases, we find asymmetric protection, with approximate to 20 by protected an one side of the core particle and no protection on the other. We demonstrated through crosslinking experiments that the result is not due to any sliding of the histone core caused by either linker histone addition or micrococcal nuclease cleavage, Because the core particle is itself it symmetric object, the preferred asymmetric location of a linker histone must be dictated by unknown elements in the DNA sequence.