A large portion of the eukaryotic genome is packaged into transcriptionally 
silent heterochromatin. Several factors that play important roles during the 
establishment and maintenance of this condensed form have been identified. 
Methylation of lysine 9 within histone H3 and the subsequent binding of the 
chromodomain protein heterochromatin protein 1 (HP1) are thought to initiate 
heterochromatin formation in vivo and to propagate a heterochromatic state 
lasting through several cell divisions. For the present study we analyzed the 
binding of HP1 to methylated chromatin in a fully reconstituted system. In 
contrast to its strong binding to methylated peptides, HP1 binds only weakly to 
methylated chromatin. However, the addition of recombinant SU(VAR) protein, such 
as ACF1 or SU(VAR)3-9, facilitates HP1 binding to chromatin methylated at lysine 
9 within the H3 N terminus (H3K9). We propose that HP1 has multiple target sites 
that contribute to its recognition of chromatin, only one of them being 
methylated at H3K9. These findings have implications for the mechanisms of 
recognition of specific chromatin modifications in vivo.