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 [1,2].
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 .
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 organization [2,3,4]. The SAF-A protein is cleaved by
caspase-3 during apoptosis [2,5].
Mammalian Acinus, a protein which induces apoptotic chromatin condensation
after cleavage by caspase-3 . Acinus also contains a RNA-recognition
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
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 . 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 .
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 homolog of RAD18.
The profile we developed cover the entire SAP motif.
February 2003 / First entry.
PROSITE method (with tools and information) covered by this documentation:
Aravind L., Koonin E.V.
SAP - a putative DNA-binding motif involved in chromosomal organization.
Distinct roles of the NH2- and COOH-terminal domains of the protein inhibitor of activated signal transducer and activator of transcription (STAT) 1 (PIAS1) in cytokine-induced PIAS1-Stat1 interaction.
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