[5][6] This gene encodes a protein with an important role in the apoptotic (programmed cell death) pathway induced by the CD27 antigen, a member of the tumor necrosis factor receptor (TFNR) superfamily.

The CD27 antigen cytoplasmic tail binds to the N-terminus of this protein.

Two alternatively spliced transcript variants encoding distinct proteins have been described.

[5] Siva protein is a zinc-containing intracellular ligand of the CD4 receptor that promotes HIV-1 envelope-induced apoptosis in T-lymphoid cells.

Recent research has demonstrated that Siva is a direct transcriptional target for the tumor-suppressors p53 and E2F1.