DNAs coding for human cell surface antigen (Fas or Fas antigen), vectors for expressing for said DNAs and transformants transfected with said vector are proveded. Fas is a polypeptide that exists in the surfaces of a variety of cells and is considered to be deeply concerned with the apoptosis of cells. The isolated Fas cDNA has an open reading frame that is capable of encoding a protein consisting of 335 amino acids. The mature Fas antigen is a protein consisting of 319 amino acids having a calculated molecular weight of about 36,000 and is constituted by an extracellular domain of 157 amino acids, a membrane-spanning domain of 17 amino acids, and a cytoplasmic domain of 145 amino acids.