PROSITE documentation PDOC00905
Initiation factor 2 signature


Initiation factor 2 (IF-2) (gene infB) [1] is one of the three factors required for the initiation of protein biosynthesis in bacteria. IF-2 promotes the GTP-dependent binding of the initiator tRNA to the small subunit of the ribosome. IF-2 is a protein of about 70 to 95 Kd which contains a central GTP-binding domain flanked by a highly variable N-terminal domain and a more conserved C-terminal domain.

Bacterial IF-2 is structurally and functionally related to eukaryotic mitochondrial IF-2 (IF-2(mt)) [2] as well as to algal and plants chloroplast IF-2 (IF-2(chl)). Both IF-2(mt) and IF-2(chl) are encoded by nuclear genes and are produced as precursor proteins with a transit peptide. An exception are red algae where IF-2(chl) is encoded by the plastid genome [3].

As a signature pattern, we selected a conserved region in the C-terminal section of these proteins.


Proteins belonging to this family also contain a copy of the ATP/GTP- binding motif 'A' (P-loop) (see <PDOC00017>).

Last update:

April 2006 / Pattern revised.


Technical section

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

IF2, PS01176; Initiation factor 2 signature  (PATTERN)


1AuthorsLaalami S. Sacerdot C. Vachon G. Mortensen K. Sperling-Petersen H.U. Cenatiempo Y. Grunberg-Manago M.
TitleStructural and functional domains of E coli initiation factor IF2.
SourceBiochimie 73:1557-1566(1991).
PubMed ID1805969

2AuthorsMa L. Spremulli L.L.
TitleCloning and sequence analysis of the human mitochondrial translational initiation factor 2 cDNA.
SourceJ. Biol. Chem. 270:1859-1865(1995).
PubMed ID7829522

3AuthorsKostrzewa M. Zetsche K.
TitleOrganization of plastid-encoded ATPase genes and flanking regions including homologues of infB and tsf in the thermophilic red alga Galdieria sulphuraria.
SourcePlant Mol. Biol. 23:67-76(1993).
PubMed ID8219057

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