In biology, the PYLIS downstream sequence (PYLIS: ''pyrrolysine insertion sequence'') is a
stem-loop
Stem-loop intramolecular base pairing is a pattern that can occur in single-stranded RNA. The structure is also known as a hairpin or hairpin loop. It occurs when two regions of the same strand, usually complementary in nucleotide sequence wh ...
structure that appears on some
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 ...
sequences. This
structural motif
In a chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a common three-dimensional structure that appears in a variety of different, evolutionarily unrelated molecules. A structural motif does not have t ...
was previously thought to cause the UAG (amber)
stop codon
In molecular biology (specifically protein biosynthesis), a stop codon (or termination codon) is a codon ( nucleotide triplet within messenger RNA) that signals the termination of the translation process of the current protein. Most codons in ...
to be translated to the
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
pyrrolysine
Pyrrolysine (symbol Pyl or O; encoded by the 'amber' stop codon UAG) is an α-amino acid that is used in the biosynthesis of proteins in some methanogenic archaea and bacteria; it is not present in humans. It contains an α-amino group (which ...
instead of ending the protein translation.
However, it has been shown that PYLIS has no effect upon the efficiency of the UAG suppression,
hence even its name is, in fact, incorrect.
See also
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SECIS element
References
Further reading
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External links
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Cis-regulatory RNA elements
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