PROSITE documentation PDOC00607
Prokaryotic-type class I peptide chain release factors signature


Peptide chain release factors (RFs) are required for the termination of protein biosynthesis [1]. At present two classes of RFs can be distinguished. Class I RFs bind to ribosomes that have encountered a stop codon at their decoding site and induce release of the nascent polypeptide. Class II RFs are GTP-binding proteins that interact with class I RFs and enhance class I RF activity.

In prokaryotes there are two class I RFs that act in a codon specific manner [2]: RF-1 (gene prfA) mediates UAA and UAG-dependent termination while RF-2 (gene prfB) mediates UAA and UGA-dependent termination. RF-1 and RF-2 are structurally and evolutionary related proteins which have been shown [3] to make up a family that also contains the following proteins:

  • Fungal MRF1, a mitochondrial RF (m-RF) which recognizes the UAA and UAG codons.
  • Escherichia coli RF-H, a protein of unknown function.
  • Escherichia coli hypothetical protein yaeJ and a close Pseudomonas putida homolog.

We use as a signature pattern a highly conserved region located in the central part of the 40 to 45 Kd RF-1/2 and m-RF and in the N-terminal of the 15 to 16 Kd RF-H and yaeJ.


Prokaryotic-type class I RFs display no significant sequence similarity to prokaryotic-type class II which belong to the family of GTP-binding elongation factors (see <PDOC00273>) nor to eukaryotic class I or class II RFs.

Expert(s) to contact by email:

Tate W.P.

Last update:

December 2004 / Pattern and text revised.


Technical section

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

RF_PROK_I, PS00745; Prokaryotic-type class I peptide chain release factors signature  (PATTERN)


1AuthorsTate W.P. Poole E.S. Mannering S.M.
SourceProg. Nucleic Acids. Res. Mol. Biol. 52:293-335(1996).

2AuthorsCraigen W.J. Lee C.C. Caskey C.T.
TitleRecent advances in peptide chain termination.
SourceMol. Microbiol. 4:861-865(1990).
PubMed ID2215213

3AuthorsPel H.J. Rep M. Grivell L.A.
TitleSequence comparison of new prokaryotic and mitochondrial members of the polypeptide chain release factor family predicts a five-domain model for release factor structure.
SourceNucleic Acids Res. 20:4423-4428(1992).
PubMed ID1408743

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