- Ribosome Recycling Factor
Name = mitochondrial ribosome recycling factor
HGNCid = 7234
Symbol = MRRF
EntrezGene = 92399
OMIM = 604602
RefSeq = NM_138777
UniProt = Q96E11
Chromosome = 9
Arm = q
Band = 32
LocusSupplementaryData = -q34.1
Ribosome Recycling Factor (RRF) is a
proteinfound in bacterialcells as well as eukaryotic organelles, specifically mitochondriaand chloroplasts. It functions to recycle ribosomesafter completion of protein synthesis.
RRF was disocvered in the early 1970s by the groundbreaking work [Hiroshima and Kaji (1970) "Factor Dependent Breakdown of Polysomes" [http://www.elsevier.com/wps/find/journaldescription.cws_home/622790/description#description BBRC] Vol. 41(4), 977-883.] [Hirashima and Kaji (1972) "Factor-dependent Release of Ribosomes from Messenger RNA. Requirement for Two Heat-Stable Factors" [http://www.elsevier.com/wps/find/journaldescription.cws_home/622890/description#description Journal of Molecular Biology] Vol. 65(1), 43-58.] [Hirashima and Kaji (1972) "Purification and Properties of Ribosome-Releasing Factor" [http://acsinfo.acs.org/journals/bichaw/ Biochemistry] Vol. 11(22), 4037-4044.] [Hirashima and Kaji (1973) "Role of Elongation Factor G and a Protein Factor on the Release of Ribosomes from Messenger Ribonucleic Acid" [http://www.jbc.org/ Journal of Biological Chemistry] Vol. 248(21), 7580-7587.] of [http://www.med.upenn.edu/camb/faculty/mv/kaji.html Akira Kaji] and Akikazu Hiroshima at the
University of Pennsylvania. Their work described the requirement for two protein factors to release ribosomes from mRNA. These two factors were identified as RRF, an unknown proteinuntil then, and Elongation Factor G (EF-G), a protein already identified and known to function in protein synthesis. RRF was originally called Ribosome "Releasing" Factor but is now called Ribosome "Recycling" Factor.
Recent evidence suggests RRF may accomplish the recycling of ribosomes by splitting ribosomes into subunits, thereby releasing the bound
mRNA[Hirokawa "et al." (2006) "The Ribosome Recycling Step: Consensus or Controversy?" [http://www.trends.com/tibs/default.htm Trends in Biochemical Sciences] Vol. 31(3), 143-149.] .
Loss of RRF Function:
Bacteria(specifically Escherichia coli), loss of the geneencoding RRF is deleterious [Janosi "et al." (1994) " Ribosome recycling factor(ribosome releasing factor) is essential for bacterial growth" [http://www.pnas.org PNAS] Vol. 91(10), 4249-4253.] . This makes RRF a possible target for new antibacterialdrugs.
Yeast mitochondrialRRF (mtRRF) is encoded by a gene in the cell nucleus. Loss of function of this geneleads to mitochondrial genomeinstability and respiratoryincompetence [Teyssier "et al." (2003) "Temperature-sensitive mutation in yeast mitochondrial ribosome recycling factor (RRF)" [http://nar.oxfordjournals.org/ NAR] Vol. 31(14), 4218-4226.] .
Structure of RRF and Binding to Ribosomes
The crystal structure of RRF was first determined by
X-ray diffractionin 1999 [Selmer "et al." (1999) "Crystal structure of Thermotoga maritima ribosome recycling factor: a tRNA mimic" [http://www.sciencemag.org Science] Vol. 286(5448), 2349-2352.] . The most striking revelation was that RRF is a near-perfect structural mimicof tRNA, in both size and dimensions. One view of RRF can be seen [http://www.pharm.kyoto-u.ac.jp/structbl/gallery/structure/rrf.jpghere] .
Despite the tRNA-mimicry, RRF binds to
ribosomesquite differently from the way tRNAdoes [Agrawal "et al." (2004) "Visualization of ribosome-recycling factor on the Escherichia coli 70S ribosome: Functional implications" [http://www.pnas.org PNAS] , Vol. 101(24), 8900-8905.] . It has been suggested that ribosomes bind proteins (or protein domain) of similar shape and size to tRNA, and this, rather than function, explains the observed structural mimicry.
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