This entry represents the RNA recognition motif (RRM) of RNPS1 and its eukaryotic homologues. RNPS1 was originally characterised as a general pre-mRNA splicing activator, which activates both constitutive and alternative splicing of pre-mRNA in vitro []. It has been identified as a protein component of the splicing-dependent mRNP complex, or exon-exon junction complex (EJC), and is directly involved in mRNA surveillance [, ]. Furthermore, RNPS1 is a splicing regulator whose activator function is controlled in part by CK2 (casein kinase II) protein kinase phosphorylation []. It can also function as a squamous-cell carcinoma antigen recognized by T cells-3 (SART3)-binding protein, and is involved in the regulation of mRNA splicing []. RNPS1 contains an N-terminal serine-rich (S) domain, a central RNA recognition motif (RRM), and the C-terminal arginine/serine/proline-rich (R/S/P) domain.
This entry represents the RNA recognition motif (RRM) of Acinus (called 'Apoptotic chromatin condensation inducer in the nucleus' or ACIN1). Acinus was first identified as a target of proteolytic cleavage during apoptosis and has been implicated in transcriptional control []. Later, it was found to be part of the ASAP complex (consists of Acinus, RNPS1 and SAP18) that interacts with the exon-junction complex (EJC), a messenger ribonucleoprotein complex involved in post-transcriptional regulation. The ASAP complex serves as an auxiliary component of EJC deposited at splice junction on mRNAs [, ]. Acinus contains a P-loop motif and an RNA recognition motif (RRM).
This superfamily includes several eukaryotic Sin3 associated polypeptide p18 (SAP18) sequences. SAP18 is known to be a component of the Sin3-containing complex which is responsible for the repression of transcription via the modification of histone polypeptides []. SAP18 (UBL domain) is one of the three three ASAP subunits (along with Acinus (β-hairpin motif) and RNPS1 (RRM domain)) that play a role in programmed cell death, transcriptional regulation, pre-mRNA splicing and mRNA quality control [, ]. The ASAP complex interacts with the exon-junction complex (EJC), a messenger ribonucleoprotein complex involved in post-transcriptional regulation [].The high degree of evolutionary conservation and the fortuitous crystal contacts at the α-β groove suggest that this surface of SAP18 is a hot spot for interactions. Possible binding partners targeting this surface of SAP18 are transcription factors (such as Bicoid and Kruppel) and/or Sin3a-HDAC subunits.
This entry represents the RNA recognition motif 1 (RRM1) of SART3 (also known as Tip110), which is an RNA-binding protein expressed in the nucleus of the majority of proliferating cells, including normal cells and malignant cells, but not in normal tissues except for the testes and fetal liver []. It is involved in the regulation of mRNA splicing probably via its complex formation with RNPS1 (an RNA-binding protein with a serine-rich domain), a pre-mRNA-splicing factor []. SART3 has also been identified as a nuclear Tat-interacting protein that regulates Tat transactivation activity through direct interaction and functions as an important cellular factor for HIV-1 gene expression and viral replication []. In addition, SART3 is required for U6 snRNP targeting to Cajal bodies []. It binds specifically and directly to the U6 snRNA, interacts transiently with the U6 and U4/U6 snRNPs, and promotes the reassembly of U4/U6 snRNPs after splicing in vitro [].SART3 contains an N-terminal HAT (half-a-tetratricopeptide repeat)-rich domain, a nuclearlocalization signal (NLS) domain, and two C-terminal RNA recognition motifs (RRMs).
This entry represents the RNA recognition motif 2 (RRM2) of SART3 (also known as Tip110), which is an RNA-binding protein expressed in the nucleus of the majority of proliferating cells, including normal cells and malignant cells, but not in normal tissues except for the testes and fetal liver []. It is involved in the regulation of mRNA splicing probably via its complex formation with RNPS1 (an RNA-binding protein with a serine-rich domain), a pre-mRNA-splicing factor []. SART3 has also been identified as a nuclear Tat-interacting protein that regulates Tat transactivation activity through direct interaction and functions as an important cellular factor for HIV-1 gene expression and viral replication []. In addition, SART3 is required for U6 snRNP targeting to Cajal bodies []. It binds specifically and directly to the U6 snRNA, interacts transiently with the U6 and U4/U6 snRNPs, and promotes the reassembly of U4/U6 snRNPs after splicing in vitro [].SART3 contains a HAT (N-terminal half-a-tetratricopeptide repeat)-rich domain, a nuclearlocalization signal (NLS) domain, and two C-terminal RNA recognition motifs (RRMs).
