Amber codons

Can exposure of E. coli to nitrous acid (HN02) lead to mutation of a tRNAGLY to an amber suppressor The Gly codons are GGX (where X = any nucleotide) and the amber codon is UAG. 

SCHEME 19.7 Amber codon suppression strategy for unnatural azido amino acid incorporation in proteins. 

Basu, A.K., Niedemhofer, L.J., and Essigmann, J.M. (1987) Deoxyhexanu-cleotide containing a vinyl chloride induced DNA lesion, 1. JV -ethenoade-nine synthesis, physical characterization, and incorporation into a duplex bacteriophage M13 genome as part of an amber codon. Biochemistry, 26, 5626-5635. 

The second key step for the expansion of the biosynthesizing system to introduce nonnatural amino acids is the expansion of the genetic codes. Schultz [38] and Chamberlin [39] first assigned an amber (UAG) stop codon to a nonnatural amino acid (aa ). By adding an aa -tRNA with a CUA anticodon as a suppressor of the amber codon, they successfully introduced the nonnatural amino acid at that position. Since then, the amber suppression method has been employed by a number of researchers. This method is advantageous in that an unsuccessful decoding of the UAG codon automatically leads to... 

Similar to the amber codon method, four-base codon method has been shown to work in living cells [55]. 

In the genetic code, UAG is a stop codon. It is known as the amber codon. 

The nonsense snppression mutagenesis entails mutating a codon of interest to the nonsense stop codon, TAG (amber). This is followed by in vitro transcription of UAG-containing mRNA which directs the incorporation of modified/unnatural amino acid (m/u-amino acid) during in vitro or in vivo (by connecting mRNA and m/u-acyl tRNA) translation. The m/u-amino acid is aminoacy-lated onto the snppressor tRNA with anticodon, CUA which recognizes the amber codon on the mRNA. Adapted from Cornish and Schultz (1994)... 

Huber, T., Naganathan, S., Tian, H., Ye, S., Sakmar, T. P. (2013). Unnatural amino acid mutagenesis of GPCRs using amber codon suppression and bioorthogonal labeling. In P. M. Conn (Ed.), Methods in Enzymology Vol. 520 (pp. 281—305) Academic Press. http //www.sciencedirect.eom/science/bookseries/00766879/520/supp/C. 

Amber codon, nonsense codon the sequence UAG in mRNA. It does not code for any of the 20 proteogenic amino acids, and it results in the termination of protein synthesis (premature termination when UAG is produced by mutation of a sense codon). Potential precursors for the production of UAG by mutation are UCG (serine), UAU and UAC (tyrosine) and CAG (glutamine). 

Amber mutants mutant bacteria in which the mRNA contains the codon UAG as a result of a point mutation (see Amber codon). The mutation is not necessarily lethal, because a compensatory suppressor mutation in a tRNA may enable the protein synthesizing system to recognize the amber codon as a sense codon. The term amber was arbitrarily chosen by the discoverer of A. m. 

Nonsense codon an Amber codon (see), or Ochre codon (see). 

Ochre codon the UAA sequence in mRNA. Like the amber codon, it signals the end of protein biosynthesis. The synthesized polypeptide chain is released after the incorporation of the amino acid encoded immediately before the 0.c. Ochre is probably the natural termination codon, and the one most widely employed by all living systems. See Ochre muttmts Ochre mutants bacterial mutants, which, as a result of a point mutation, possess a UAA codon in their mRNA (see Ochre codon). There are specific Suppressors (see) of ochre mutations. 

Termination codon, stop codon, punctuation codon a sequence of three nucleotides in mRNA, which signals the end of polypeptide synthesis and release of the polypeptide in the process of Protein biosynthesis (see). 5 -tlAA (see Ochre codon), 5 -UAG (see Amber codon) and UGA are T.c. 

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