In this project, we stably expressed His-SUMO3 in control and SENP1-depleted HEK293T cells. After the cells were infected with Sendai virus, we lysed cells by 8 M urea, purified SUMO3-associated proteins through His-tag pulldown using Ni-NTA agarose, and then utilized mass spectrometry to identify SUMOylated proteins in control and SENP1-depleted cells.