In biology, the PYLIS downstream sequence (PYLIS: pyrrolysine insertion sequence) is a stem-loop structure that appears on some mRNA sequences. This structural motif was previously thought to cause the UAG (amber) stop codon to be translated to the amino acidpyrrolysine 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.
^Théobald-Dietrich A, Giegé R, Rudinger-Thirion J (2005). "Evidence for the existence in mRNAs of a hairpin element responsible for ribosome dependent pyrrolysine insertion into proteins". Biochimie. 87 (9-10): 813–7. doi:10.1016/j.biochi.2005.03.006. PMID16164991.
^Zhang Y, Baranov PV, Atkins JF, Gladyshev VN (May 2005). "Pyrrolysine and selenocysteine use dissimilar decoding strategies". J. Biol. Chem. 280 (21): 20740–51. doi:10.1074/jbc.M501458200. PMID15788401.