Histone H3 is one of the five main histone proteins involved in the structure of chromatin in eukaryotic cells. H3 is highly conserved across species, indicating its critical role in chromatin structure and function. It is subject to various post-translational modifications, including acetylation, methylation, phosphorylation, and ubiquitination, which can affect gene expression by altering chromatin structure and recruiting regulatory proteins. These modifications are key components of epigenetic mechanisms that regulate gene activity without altering the underlying DNA sequence. Besides, Peptidylprolyl Isomerase E (PPIE) has been identified as an interactor of H3, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human H3 and recombinant mouse PPIE. Briefly, H3 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to PPIE-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-H3 pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µL stop solution to the wells and read at 450/630 nm immediately. The binding activity of recombinant human H3 and recombinant mouse PPIE was shown in Figure 1, the EC50 for this effect is 2.40 ug/mL.