Relatively speaking

Protein X is a signalling molecule that stimulates apoptosis. Treatment of cells with Protein X results in five times higher levels of cell death than those seen in untreated cells (wild type), as measured by Caspase-positive cells. Based on previous work, the authors identify Protein Y as the putative receptor for Protein X and here try to test whether this is indeed the case. They claim that in a geneY mutant, where no receptor is expressed, treatment with Protein X no longer results in increased cell death, supporting the hypothesis that Protein Y is the receptor for signalling molecule X.