The combination of baculovirus-mediated gene delivery (BacMam) with LanthaScreen® Cellular Assay technology enables a platform for the analysis of specific posttranslational modifications of various substrates including p53. BacMam provides a convenient genetic delivery tool for a GFP-p53 fusion protein in the cell line of interest. This kit describes an HTS-compatible cellular immunoassay measuring acetylation of GFP-p53 at Lys382.