Upon bacterial delivery of plasmids, in which the TETP promoter controls the suicide gene of purine nucleoside phosphorylase (PNP) or the chimeric gene of cytosine desaminase and phosphoryl transferase (FCU1) of yeasts, the transgene is specifically expressed in B16 melanoma cells, but not in kidney COS-1 fibroblasts. Here, PNP is linked to melanoma.