The Tryptophan operon leader is an RNA element found at the 5′ of some bacterial tryptophan operons. The leader sequence can form two different structures known as the terminator and the anti-terminator, based on the Tryptophan amounts in the cell. The leader also codes for very short peptide sequence that is rich in

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α- carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...

. The terminator structure is recognised as a termination signal for

RNA polymerase In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that synthesizes RNA from a DNA template. Using the enzyme helicase, RNAP locally opens the ...

and the operon is not transcribed. This structure forms when the cell has an excess of tryptophan and

ribosome 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 ...

movement over the leader transcript is not impeded. When there is a deficiency of the charged tryptophanyl

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 ac ...

the ribosome translating the leader peptide stalls and the antiterminator structure can form. This allows

to transcribe the operon. At least 6 different amino acid operons are known to be regulated by this attenuation.

Trp RNA-binding attenuation protein

The formation of the terminator requires the trp RNA-binding attenuation

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, respo ...

(TRAP protein) in species of ''

Bacillus ''Bacillus'' (Latin "stick") is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum ''Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural ''Bacilli ...

'' and related

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 among ...

. This protein is encoded by the MtrB gene. TRAP protein forms an oligomer of 11 subunits, in the presence of tryptophan this binds to section of RNA containing 11 (G/U)AG repeats. This sequence overlaps the anti-terminator loop, thus TRAP-binding preventing formation of the anti-terminator loop. When TRAP is bound the terminator loop forms and the operon is not transcribed.

Tryptophan RNA-binding attenuator protein inhibitory protein

Tryptophan RNA-binding attenuator protein inhibitory protein (Anti-TRAP protein or AT) is a short protein encoded by the rtpA in Bacillus. Synthesis of anti-TRAP is induced by uncharged tryptophan

. Anti-TRAP binds to TRAP and inhibits its binding to the tryptophan operator leader. This causes the anti-terminator loop to form and the tryptophan operon to be transcribed.

References

External links

* Cis-regulatory RNA elements {{molecular-cell-biology-stub