NOPS domain, including C-terminal coiled-coil region, in p54nrb/PSF/PSPC1 family proteins
The family contains a DBHS domain (for Drosophila behavior, human splicing), which comprises two conserved RNA recognition motifs (RRMs), also termed RBDs (RNA binding domains) or RNPs (ribonucleoprotein domains), and a charged protein-protein interaction NOPS (NONA and PSP1) domain. This model corresponds to the NOPS domain, with a long helical C-terminal extension, found in the p54nrb/PSF/PSPC1 proteins. The NOPS domain specifically binds to the second RNA recognition motif (RRM2) domain of the partner DBHS protein via a substantial interaction surface. Its highly conserved C-terminal residues are critical for functional DBHS dimerization while the highly conserved C-terminal helical extension, forming a right-handed antiparallel heterodimeric coiled-coil, is essential for localization of these proteins to subnuclear bodies. Members in the family include 54 kDa nuclear RNA- and DNA-binding protein (p54nrb), polypyrimidine tract-binding protein (PTB)-associated-splicing factor (PSF) and paraspeckle protein component 1 (PSPC1 or PSP1), which are ubiquitously expressed and are conserved in vertebrates. p54nrb, also termed NONO or NMT55, is a multi-functional protein involved in numerous nuclear processes including transcriptional regulation, splicing, DNA unwinding, nuclear retention of hyperedited double-stranded RNA, viral RNA processing, control of cell proliferation, and circadian rhythm maintenance. PSF, also termed POMp100, is a multi-functional protein that binds RNA, single-stranded DNA (ssDNA), double-stranded DNA (dsDNA) and many factors, and mediates diverse activities in the cell. PSPC1 is a novel nucleolar factor that accumulates within a new nucleoplasmic compartment, termed paraspeckles, and diffusely distributes in the nucleoplasm. The cellular function of PSPC1 remains unknown currently. PSF has an additional large N-terminal domain that differentiates it from other family members.
Jiyao W et al.(2023). "The conserved domain database in 2023.",