This family consists of 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 is also present in the ASAP complex which is thought to be involved in the regulation of splicing during the execution of programmed cell death [].
Histone acetylation plays a key role in the regulation of gene expression. The chromatin structure and accessibility of genes to transcription factors isregulated by enzymes that acetylate and deacetylate histones. The Sin3A-histone deacetylase (HDAC) co-repressor complex consists of multiple proteins and regulates gene expression by deacetylating histones.This group represents the Histone deacetylase complex subunit SAP18 (Sin3A associated protein 18) []. SAP18 adopts an ubiquitin-like fold with several large loop insertions [].
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.
The RSB motif on the Acinus (also known as Acin1) protein is the core around which the ASAP complex is built. The apoptosis and splicing-associated protein complex, ASAP, is made up of three proteins, SAP18 (Sin3-associated protein of 18kDa), RNA-binding protein S1 (RNPS1) and apoptotic chromatin inducer in the nucleus (Acinus). The ASAP complex appears to be an assembly of proteins at the interface between transcription, splicing and nonsense-mediated mRNA decay (NMD), acting as a hub in the network of protein-interactions that regulate gene-expression [].
