Death domain (DD) found in the Nuclear Matrix Protein P84 (also known as HPR1 or THOC1). HPR1/p84 resides in the nuclear matrix and is part of the THO complex, also called TREX (transcription/export) complex, which functions in mRNP biogenesis at the interface between transcription and export of mRNA from the nucleus. Mice lacking THOC1 have abnormal testis development and are sterile. In general, DDs are protein-protein interaction domains found in a variety of domain architectures. Their common feature is that they form homodimers by self-association or heterodimers by associating with other members of the DD superfamily including CARD (Caspase activation and recruitment domain), DED (Death Effector Domain), and PYRIN. They serve as adaptors in signaling pathways and can recruit other proteins into signaling complexes.