Ribosome recycling factor or ribosome release factor (RRF) is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

found in

bacterial Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

cells as well as

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...

organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' t ...

s, specifically mitochondria and

chloroplasts A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it i ...

. It functions to recycle ribosomes after completion of

protein synthesis Protein biosynthesis (or protein synthesis) is a core biological process, occurring inside cells, balancing the loss of cellular proteins (via degradation or export) through the production of new proteins. Proteins perform a number of critical ...

( bacterial translation). In humans, the mitochrondrial version is coded by the MRRF gene.

Discovery

The ribosome recycling factor was discovered in the early 1970s by the work of Akira Kaji and Akikazu Hiroshima at the

University of Pennsylvania The University of Pennsylvania (also known as Penn or UPenn) is a private research university in Philadelphia. It is the fourth-oldest institution of higher education in the United States and is ranked among the highest-regarded universit ...

. Their work described the requirement for two protein factors to release ribosomes from

mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...

. These two factors were identified as RRF, an unknown

until then, and Elongation Factor G (EF-G), a protein already identified and known to function in

. RRF was originally called Ribosome ''Releasing'' Factor but is now called Ribosome ''Recycling'' Factor.

Function

RRF accomplishes the recycling of ribosomes by splitting ribosomes into subunits, thereby releasing the bound

. This also requires the participation of

EF-G EF-G (elongation factor G, historically known as translocase) is a prokaryotic elongation factor involved in protein translation. As a GTPase, EF-G catalyzes the movement (translocation) of transfer RNA (tRNA) and messenger RNA (mRNA) thro ...

( GFM2 in humans). Depending on the tRNA, IF1– IF3 may also perform recycling.

Loss of RRF function

*In

Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

(specifically ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...

''), loss of the

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

encoding RRF is deleterious. This makes RRF a possible target for new

antibacterial An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...

drugs. *

Yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to consti ...

mitochondrial A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

RRF (mtRRF) is encoded by a gene in the cell nucleus. Loss of function of this

leads to mitochondrial

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...

instability and

respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gre ...

incompetence.

Structure and binding to ribosomes

The crystal structure of RRF was first determined by X-ray diffraction in 1999. The most striking revelation was that RRF is a near-perfect structural mimic of

tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino a ...

, in both size and dimensions. One view of RRF can be see
here
Despite the tRNA-mimicry, RRF binds to

ribosomes Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to ...

quite differently from the way

does. It has been suggested that ribosomes bind proteins (or

protein domain In molecular biology, a protein domain is a region of a protein's polypeptide chain that is self-stabilizing and that folds independently from the rest. Each domain forms a compact folded three-dimensional structure. Many proteins consist o ...

) of similar shape and size to tRNA, and this, rather than function, explains the observed structural mimicry.

References

External links