Abstract: The present invention provides a novel cDNA sequence (Pem), a gene product protein (Seq. id No. 1), and uses for this novel cDNA Sequence and the Pem gene product. The DNA sequence and recombinant DNA molecules of this invention are characterized in that each codes for a novel protein having the following characteristics: (1) is expressed by T lymphoma cells, (2) is not expressed in normal thymus, activated spleen cells, gut associated lymphoid tissue, or bone marrow, and is not detectable in adult brain, liver, large intestine or ovary, (3) is expressed in immortalized or cancerous cell lines, and (4) is expressed in embryonic development.