The technology relates to a nucleic acid expression cassette comprising a TR element encoding an mRNA molecule that is translated in stressed and/or dying cells, and a nucleotide sequence operably linked to the TR element, that is a first open reading frame (ORF) sequence and encodes a polypeptide or a fragment thereof and is co-translated with the TR element. The technology further relates to mammalian cells and a transgenic animal comprising such expression cassette. Further included are kits comprising the expression cassette, and methods for determining toxicity, and killing a target cell.