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An example of a single base deletion forming a stop codon. Hidden stops are non-stop codons that would be read as stop codons if they were frameshifted +1 or −1. These prematurely terminate translation if the corresponding frame-shift (such as due to a ribosomal RNA slip) occurs before the hidden stop.
Three translation tables have a peculiar status: Table 7 is now merged into translation table 4. Table 8 is merged to table 1; all plant chloroplast differences due to RNA edit.
Alternative start codons depending on the organism include "GUG" or "UUG"; these codons normally represent valine and leucine, respectively, but as start codons they are translated as methionine or formylmethionine. [33] The three stop codons have names: UAG is amber, UGA is opal (sometimes also called umber), and UAA is ochre. Stop codons are ...
There are 64 different codons in the genetic code and the below tables; most specify an amino acid. [6] Three sequences, UAG, UGA, and UAA, known as stop codons, [note 1] do not code for an amino acid but instead signal the release of the nascent polypeptide from the ribosome. [7]
The ambush hypothesis is a hypothesis in the field of molecular genetics that suggests that the prevalence of “hidden” or off-frame stop codons in DNA selectively deters off-frame translation of mRNA to save energy, molecular resources, and to reduce strain on biosynthetic machinery by truncating the production of non-functional, potentially cytotoxic protein products. [1]
However, at least in humans it has now been shown that AGA and AGG sequences are not recognized as termination codons. A -1 mitoribosome frameshift occurs at the AGA and AGG codons predicted to terminate the CO1 and ND6 open reading frames (ORFs), and consequently both ORFs terminate in the standard UAG codon.
NMD is a cellular mechanism that degrades mRNAs containing premature termination codons (PTCs), which can arise from mutations. Comprehensive analyses large scale genetics and gene expression datasets have enabled the systemic identification of the complex rules governing NMD efficiency, and quantification of their relative importance and effect size. [10]
The two other start codons listed by table 1 (GUG and UUG) are rare in eukaryotes. [3] Prokaryotes have less strigent start codon requirements; they are described by NCBI table 11 . B ^ ^ ^ The historical basis for designating the stop codons as amber, ochre and opal is described in an autobiography by Sydney Brenner [ 4 ] and in a historical ...