Spatial arrangement of histones

A model for nucleosome with (H3)2.(H4)2 forming a kernel
Fig. 27.9. A model for nucleosome with (H3)2.(H4)2 forming a kernel.
Arrangement of four histones in the nucleosome was also studied through a study of specific sites in DNA and of their interaction with four histones. These sites could be assigned to specific regions of octamer and, therefore arrangement of eight histone molecules could be described. It was shown that (H3)2.(H4)2 tetramer defines the central turn of the DNA superhelix. H2A and H2B are added as two (H2A).(H2B) dimers one on each face of the tetramer (H3)2.(H4)2 and each binding additional DNA and completing the superhelix (Fig. 27.9). (H3)2 (H4)2. tetramer makes a central 'kernel' associated with two independent dimers H2A-H2B. This explains, why H3 and H4 alone can confer nucleosome like properties on DNA but H2A and H2B can not confer this property.
A model for nucleosome with (H3)2.(H4)2 forming a kernel
Fig. 27.9. A model for nucleosome with (H3)2.(H4)2 forming a kernel.