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 chro matosomal DNA by the presence of a linker histone (H1 degrees) has bee n quantitatively measured in two reconstituted systems. We have used c hromatosomes reconstituted at two distinct positions on a DNA fragment containing the 5S rRNA gene from Lytechinus variegatus and at a speci fic position on a sequence containing Ga14- and USF-binding sites, In all cases, we find asymmetric protection, with approximate to 20 by pr otected an one side of the core particle and no protection on the othe r. We demonstrated through crosslinking experiments that the result is not due to any sliding of the histone core caused by either linker hi stone addition or micrococcal nuclease cleavage, Because the core part icle is itself it symmetric object, the preferred asymmetric location of a linker histone must be dictated by unknown elements in the DNA se quence.