A gene that can be introduced into target cells that will, under the appropriate conditions, lead to destruction of that cell. The herpes simplex virus type 1 thymidine kinase gene ( HSV1-tk) is an example of a suicide gene. It encodes a protein that, in the presence of pro-drugs such as ganciclovir, leads to cell death. Suicide-gene-therapy approaches have been attempted as a way to destroy cancer cells.