RNA recognition motif 1 (RRM1) found in vertebrate polypyrimidine tract-binding protein (PTB)-associated-splicing factor (PSF)This subgroup corresponds to the RRM1 of PSF, also termed proline- and glutamine-rich splicing factor, or 100 kDa DNA-pairing protein (POMp100), or 100 kDa subunit of DNA-binding p52/p100 complex, a multifunctional protein that mediates diverse activities in the cell. It is ubiquitously expressed and highly conserved in vertebrates. PSF binds not only RNA but also both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) and facilitates the renaturation of complementary ssDNAs. Besides, it promotes the formation of D-loops in superhelical duplex DNA, and is involved in cell proliferation. PSF can also interact with multiple factors. It is an RNA-binding component of spliceosomes and binds to insulin-like growth factor response element (IGFRE). PSF functions as a transcriptional repressor interacting with Sin3A and mediating silencing through the recruitment of histone deacetylases (HDACs) to the DNA binding domain (DBD) of nuclear hormone receptors. Additionally, PSF is an essential pre-mRNA splicing factor and is dissociated from PTB and binds to U1-70K and serine-arginine (SR) proteins during apoptosis. PSF forms a heterodimer with the nuclear protein p54nrb, also known as non-POU domain-containing octamer-binding protein (NonO). The PSF/p54nrb complex displays a variety of functions, such as DNA recombination and RNA synthesis, processing, and transport. PSF contains two conserved RNA recognition motifs (RRMs), also termed RBDs (RNA binding domains) or RNPs (ribonucleoprotein domains), which are responsible for interactions with RNA and for the localization of the protein in speckles. It also contains an N-terminal region rich in proline, glycine, and glutamine residues, which may play a role in interactions recruiting other molecules.