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Saturation mutagenesis is commonly achieved by site-directed mutagenesis PCR with a randomised codon in the primers (e.g. SeSaM) [2] or by artificial gene synthesis, with a mixture of synthesis nucleotides used at the codons to be randomised. [3] Different degenerate codons can be used to encode sets of amino acids. [1]
Degeneracy or redundancy [1] of codons is the redundancy of the genetic code, exhibited as the multiplicity of three-base pair codon combinations that specify an amino acid. The degeneracy of the genetic code is what accounts for the existence of synonymous mutations . [ 2 ] :
Codon usage bias in Physcomitrella patens. Codon usage bias refers to differences in the frequency of occurrence of synonymous codons in coding DNA. A codon is a series of three nucleotides (a triplet) that encodes a specific amino acid residue in a polypeptide chain or for the termination of translation (stop codons).
Protein translation involves a set of twenty amino acids.Each of these amino acids is coded for by a sequence of three DNA base pairs called a codon.Because there are 64 possible codons, but only 20-22 encoded amino acids (in nature) and a stop signal (i.e. up to three codons that do not code for any amino acid and are known as stop codons, indicating that translation should stop), some amino ...
The experiments used mixtures with all 20 amino acids. For each individual experiment, 19 amino acids were "cold" (nonradioactive), and one was "hot" (radioactively tagged with 14 C so they could detect the tagged amino acid later). They varied the "hot" amino acid in each round of the experiment, seeking to determine which amino acids would be ...
However, in a protein-coding sequence, the DNA sequence is made up of a string of codons which correspond to amino acids. Because the genetic code is degenerate (more than one codon map to a single amino acid) and samples from the amino acids rather than the codons, the codons are not sampled uniformly thus leading to differences in the PCFs.
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]
Early attempts at mutagenesis using radiation or chemical mutagens were non-site-specific, generating random mutations. [2] Analogs of nucleotides and other chemicals were later used to generate localized point mutations, [3] examples of such chemicals are aminopurine, [4] nitrosoguanidine, [5] and bisulfite. [6]