Abstract: The present invention is generally directed to the identification of mouse and human genes that inhibit the growth of a tumor and induce apoptosis in cancer cells, and to polypeptides encoded by such genes. In particular, the invention concerns the nucleotide sequence of one such tumor-inhibiting gene, tag7, and the amino acid sequence of a polypeptide encoded by tag7. The invention also provides isolated nucleic acid molecules comprising tag7 polynucleotides, and vectors and host cells comprising these isolated nucleic acid molecules. The invention also provides methods of producing tag7 polynucleotides using these nucleic acid molecules, vectors and host cells, tag7 polypeptides made by three methods and antibodies that specifically bind to the tag7 polypeptide. The invention also concerns methods of inhibiting tumor growth and inducing tumor cell apoptosis, and methods of cancer therapy, using the present tag7 nucleic acid molecules and polypeptides.