The fact that expression of this gene is an indicator of DNA damage has been exploited to construct an in vitro test for mutagenicity, the GADD45a-GFP GreenScreen HC assay. This assay consists of a cell line which has been engineered so that expression of GADD45A will lead to expression of green fluorescent protein, which can easily be detected. To test a substance for mutagenicity, it is applied to these cells and fluorescence is measured.