The SAP motif is a 35-residue motif, which has been named after SAF-A/B, Acinus and PIAS, three proteins known to contain it. The SAP motif is found in a variety of nuclear proteins involved in transcription, DNA repair, RNA processing or apoptotic chromatin degradation. As the sap motif of SAF-A has been shown to be essential for specific DNA binding activity, it has been proposed that it could … expand

The SAP motif is a 35-residue motif, which has been named after SAF-A/B, Acinus and PIAS, three proteins known to contain it. The SAP motif is found in a variety of nuclear proteins involved in transcription, DNA repair, RNA processing or apoptotic chromatin degradation. As the sap motif of SAF-A has been shown to be essential for specific DNA binding activity, it has been proposed that it could be a DNA-binding motif [ PUBMED:10694879 ].

A multiple alignment of the SAP motif reveals a bipartite distribution of strongly conserved hydrophobic, polar and bulky amino acids separated by a region that contains a glycine. Secondary structure predictions suggest that the SAP motif could form two α helices separated by a turn [ PUBMED:10694879 ].

Some proteins known to contain a SAP motif are listed below:

• Vertebrate scaffold attachment factors A and B (SAF-A/B). These two proteins are heterogeneous nuclear ribonucleoproteins (hnRNPs) that bind to AT-rich chromosomal region. It has been proposed that they couple RNA metabolism to nuclear organisation [ PUBMED:10212141 PUBMED:9671816 ]. The SAF-A protein is cleaved by caspase-3 during apoptosis [ PUBMED:10671544 ].
• Mammalian Acinus, a protein which induces apoptotic chromatin condensation after cleavage by caspase-3 [ PUBMED:10490026 ]. Acinus also contains a RNA-recognition motif.
• Eukaryotic proteins of the PIAS (protein inhibitor of activated STAT) family. These proteins interact with phosphorylated STAT dimers and inhibit STAT mediated gene activation. Deletion of the first 50 amino acid residues containing the SAP domain allows the interaction of PIAS1 with STAT1 monomer [ PUBMED:10805787 ].
• Plant poly(ADP-ribose) polymerase (PARP). PARP is a nuclear protein that catalyzes the poly(ADP-ribosyl)ation of proteins. It is involved in responses to mild and severe oxidative stresses, by mediating DNA repair and programmed cell death processes, respectively [ PUBMED:9862413 ]. PARP is tightly bound to chromatin or nuclear matrix.
• Arabidopsis thaliana Arp, an apurinic endonuclease-redox protein.
• Yeast THO1 protein. It could be involved in the regulation of transcriptional elongation by RNA polymerase II [ PUBMED:9707445 ].
• Animal Ku70. Together with Ku86, it forms a DNA ends binding complex that is involved in repairing DNA double-strand breaks.
• Yeast RAD18, a protein involved in DNA repair.
• Neurospora crassa UVS-2, the homologue of RAD18.