I am trying to prove the functionality of a protein by HAT assay where I am observing for the lysine acetylation of core histones by my recombinant protein and probing it with an acetylated lysine antibody. As negative control I am using only the core histones and acetyl coA in suitable buffer without my recombinant protein. I should not expect to see any band there but I am getting a band after western blot everytime at around 10-15 KDa. Also when i load the protein alone it is giving a band throughout the protein. The antibody is monoclonal so it should not give any non specific bands. Due to the band coming constantly in the negative control and in the protein alone, I am not able to figure out if my protein is functionally active or not. Also the recombinant protein is very unstable and is degraded in a few days after purification. Request troubleshooting in this regard and if there is any other method to confirm the functionality of my protein as it is known to be a HAT protein. Please suggest. Thanks!