Fas  is a glycoprotein with a mass estimated at 43 to 48 kDa . Fas is a member of the Tumor Necrosis Factor Receptor Superfamily (TNFRSF), and it shares a cytoplasmic motif with TNF RI, referred to as the death domain, that binds cytoplasm signaling molecules to trigger the cytoplasmic apoptotic signal . Fas is expressed to a large extent on activated T and B lymphocytes, and on malignant lymphoid cells. To a lesser extent, Fas is expressed on cells from liver, heart, kidney, ovaries, and on many other malignant cells.
Yan et al. (2005) noted that the TNFRSF6 gene contains 9 exons. They identified an antisense transcript SAF within the 12.1-kb intron 1 that is transcribed in the opposite direction as the TNFRSF6 gene.