AbstractTumor suppressor genes represent a broad class of genes that normally function in the negative regulation of cell proliferation. Loss‐of‐function mutations in these genes lead to unrestrained cell proliferation and tumor formation. A fundamental understanding of how tumor suppressor genes regulate cell proliferation and differentiation should reveal important aspects of signalling pathways and cell cycle control. A recent report describing the Drosophila tumor suppressor gene warts has implications in the study of the human myotonic dystrophy gene(1). These genes encode members of a cyclic AMP‐dependent protein kinase subfamily that includes other plant and animal orthologues.