H3K9me3 binding analysis of the isolated PHD and TTD domains of UHRF2.

UHRF1 and UHRF2 are multi-domain epigenetic proteins similar in amino acid sequence and structure. These proteins play an important role in regulating gene expression via binding histones and methylated DNA. Both proteins contain TTD and PHD domains, which bind histone H3 methylated at lysine 9 (H3K9me3). While the isolated TTD and PHD domains of UHRF1 are well characterized, the same isolated domains of UHRF2 have yet to be analyzed quantitatively. We used fluorescence polarization to quantify the binding affinities of the isolated TTD and PHD to fluorescent H3K9me3 tail peptides. We discovered that the TTD domain is the main contributor to histone binding in UHRF2. In contrast, the PHD domain is the main contributor to binding in UHRF1. Thus, we show that UHRF1 and UHRF2 have distinct mechanisms of histone binding.