Figure 7. Model suggesting how HP1 proteins may gain access to internal nucleosomal regions and control remodeling by SWI/SNF.

(A) When the chromatin is methylated on H3K9, HP1 is brought in the vicinity, attracted by the methylation mark. The interaction with the nucleosome is very dynamic. (B) Remodeling creates access to hidden HP1-binding sites on the globular domain of histone H3. (C) The exposure of the internal binding sites allows HP1 to detect the remodeling and to regulate it, gaining at the same time a more stable interaction with the nucleosome.