Fig 2.

The methylated H3K9 mainly promotes HR pathway upon DNA damage. In the absence of DNA damage, tri-methylated H3K9 by Suv39H1 can bind HP1 to maintain heterochromatin, while HP1 bind on di-methylated H3K9 site is combined with BARD1/BRCA1 to initiate HR pathway. Upon damage, phosphorylated HP1β on Thr⁵¹ by CK2 will dissociate from the H3K9me3 mark, which facilitates Tip60 to access H3K9me3. Besides, cAbl also promotes Tip60 to incorporate onto H3K9me3. And MRN complex can target Tip60 to H3K9me3 and is required to activate Tip60's acetyltransferase activity which activates ATM by acetylation.