In molecular biology, translation initiation factor IF-3 (

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 ...

infC) is one of the three factors required for the initiation of protein biosynthesis in

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

. IF-3 is thought to function as a fidelity factor during the assembly of the

ternary Ternary (from Latin ''ternarius'') or trinary is an adjective meaning "composed of three items". It can refer to: Mathematics and logic * Ternary numeral system, a base-3 counting system ** Balanced ternary, a positional numeral system, useful ...

initiation

complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...

which consists of the

30S ribosomal subunit The prokaryotic small ribosomal subunit, or 30 S subunit, is the smaller subunit of the 70S ribosome found in prokaryotes. It is a complex of the 16S ribosomal RNA (rRNA) and 19 proteins. This complex is implicated in the binding of transfer RN ...

, the initiator

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 ...

and the messenger RNA. IF-3 is a basic protein that binds to the 30S ribosomal subunit. The chloroplast homolog enhances the poly( A, U, G)-dependent binding of the initiator tRNA to its ribosomal 30s subunits. IF1–IF3 may also perform ribosome recycling. IF3 is not universally found in all bacterial species. However, in '' E. coli'', it is required for the 30S subunit to bind to the initiation site in

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 ...

. In addition, it has several other jobs including the stabilization of free 30S subunits, enables 30S subunits to bind to mRNA and checks for accuracy against the first

aminoacyl-tRNA Aminoacyl-tRNA (also aa-tRNA or charged tRNA) is tRNA to which its cognate amino acid is chemically bonded (charged). The aa-tRNA, along with particular elongation factors, deliver the amino acid to the ribosome for incorporation into the polypept ...

. It also allows for rapid codon-anticodon pairing for the initiator

to bind quickly. IF3 is required by the small subunit to form initiation complexes, but has to be released to allow the

50S The 50s decade ran from January 1, 50, to December 31, 59. It was the sixth decade in the Anno Domini/Common Era, if the nine-year period from 1 AD to 9 AD is considered as a "decade". Significant people * Claudius, Roman Emperor (AD 41� ...

subunit to bind. IF3 is made up of two domains connected by a flexible linker. Together they allow IF3 to carry out its function. Human mitochondria use a nuclear-encoded homolog MTIF3 for translation initiation. Some bacteria, chloroplasts, and mitochondria have multiple copies of IF3.

References

{{InterPro content, IPR019814 Protein domains