PROSITE documentation PDOC00987
BIR repeat signature and profile


The 'baculovirus inhibitior of apoptosis protein repeat' (BIR) [1,2] is a domain of about 70 residues arranged in tandem repeats separated by a variable length linker, that seems to confer cell death-preventing activity. It is found in proteins belonging to the IAP (inhibitor of apoptosis proteins) family. The critical motifs required for anti-apoptotic activity of IAP proteins are the BIRs. All IAP proteins contain from one to three BIRs, and all known interactions between IAPs and other proteins are mediated by one or more BIRs [3].

The BIR domain has a fold that is stabilized by zinc tetrahedrally coordinated by one histidine and three cysteine residues (see <PDB:1QBH>). The structure consists of three short α-helices and turns with the zinc packed in an unusually hydrophobic environment created by residues that are highly conserved among all BIRs. A subclass of repeats, comprising those at the C-terminus of a series of BIR repeats from IAP proteins bearing RING finger domains (see <PDOC00449>), are likely to contain a C-terminal region that form an α-helix [3].

Proteins that are known to contain this domain are listed below.

  • Baculoviruses apoptosis inhibitors (IAPs).
  • Mammalian apoptosis inhibitors 1 and 2 (IAP1 and IAP2).
  • Mammalian X-linked inhibitor of apoptosis protein (X-linked IAP).
  • Chicken IAP (ITA).
  • Human neuronal apoptosis inhibitory protein (NAIP).
  • Drosophila apoptosis inhibitors 1 and 2 (Iap1 and Iap2).
  • African Swine Fever Virus (ASFV) protein p27.

BIR contains a number of perfectly conserved residues including an histidine and three cysteines. The signature pattern for BIR spans the total length of the repeat. We also developed a profile that spans the whole repeat.

Last update:

November 2011 / Text revised.


Technical section

PROSITE methods (with tools and information) covered by this documentation:

BIR_REPEAT_2, PS50143; BIR repeat profile  (MATRIX)

BIR_REPEAT_1, PS01282; BIR repeat  (PATTERN)


1AuthorsBirnbaum M.J. Clem R.J. Miller L.K.
TitleAn apoptosis-inhibiting gene from a nuclear polyhedrosis virus encoding a polypeptide with Cys/His sequence motifs.
SourceJ. Virol. 68:2521-2528(1994).
PubMed ID8139034

2AuthorsListon P. Roy N. Tamai K. Lefebvre C. Baird S. Cherton-Horvat G. Farahani R. McLean M. Ikeda J.E. MacKenzie A. Korneluk R.G.
TitleSuppression of apoptosis in mammalian cells by NAIP and a related family of IAP genes.
SourceNature 379:349-353(1996).
PubMed ID8552191

3AuthorsHinds M.G. Norton R.S. Vaux D.L. Day C.L.
TitleSolution structure of a baculoviral inhibitor of apoptosis (IAP) repeat.
SourceNat. Struct. Biol. 6:648-651(1999).
PubMed ID10404221

PROSITE is copyrighted by the SIB Swiss Institute of Bioinformatics and distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives (CC BY-NC-ND 4.0) License, see prosite_license.html.


View entry in original PROSITE document format
View entry in raw text format (no links)