Final answer:
HP1 recruits various non-histone proteins including histone-lysine N-methyltransferases like EZH1 and EZH2, as well as other structural proteins and enzymes involved in chromatin remodeling, DNA repair, and gene regulation to maintain the heterochromatin structure.
Step-by-step explanation:
Recruitment of Proteins by HP1
Once heterochromatin protein 1 (HP1) forms a dimer in the linker region between nucleosomes, it recruits various non-histone proteins to the site. HP1 can specifically bind to methylated histones, such as histone H3 when it's methylated at lysine 9 (H3K9me), which is known to be associated with the formation of heterochromatin. Furthermore, HP1 is involved in the recruitment of enzymes responsible for DNA and histone modifications that maintain the heterochromatin structure, such as histone-lysine N-methyltransferases like EZH1 and EZH2. These methyltransferases further propagate the condensed state of heterochromatin by methylating adjacent histone H3 molecules. HP1 also interacts with various proteins involved in chromatin remodeling, DNA repair, and the regulation of gene expression.
In addition to these, HP1 can attract other structural proteins, including those that are part of the protein scaffold, such as topoisomerase, which helps maintain the three-dimensional architecture of the chromatin. Together, these interactions facilitated by HP1 contribute to the compact, densely packed nature of heterochromatin, which is essential for the regulation of gene expression and the maintenance of genomic integrity.