The Sp100 protein is a constituent of nuclear domains, also known as nuclear dots (NDs). An ND-targeting region that coincides with a homodimerization domain was mapped in Sp100. Sequences similar to the Sp100 homodimerization/ND-targeting region occur in several other proteins and constitute a novel protein motif, termed HSR domain (for homogeneously-staining region) [2]. The HSR domain has also been named ASS (AIRE, Sp-100 and Sp140) [3]. This domain is usually found at the amino terminus of proteins that contain a SAND domain Pfam:PF01342.

1: The APECED polyglandular autoimmune syndrome protein, AIRE-1, contains the SAND domain and is probably a transcription factor. Gibson TJ, Ramu C, Gemund C, Aasland R; Trends Biochem Sci 1998;23:242-244. PMID:9697411

2: The nuclear dot protein sp100, characterization of domains necessary for dimerization, subcellular localization, and modification by small ubiquitin-like modifiers. Sternsdorf T, Jensen K, Reich B, Will H; J Biol Chem. 1999;274:12555-12566. PMID:10212234

3: Isolation and characterization of the mouse Aire gene. Mittaz L, Rossier C, Heino M, Peterson P, Krohn KJ, Gos A, Morris MA, Kudoh J, Shimizu N, Antonarakis SE, Scott HS; Biochem Biophys Res Commun. 1999;255:483-490. PMID:10049735