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A nonsense suppressor is a factor which can inhibit the effect of the
nonsense mutation In genetics, a nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon, or a ''nonsense codon'' in the transcribed mRNA, and in leading to a truncated, incomplete, and usually nonfunctional protein produc ...
. Nonsense suppressors can be generally divided into two classes: a) a mutated
tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino a ...
which can bind with a termination codon on
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 t ...
; b) a mutation on
ribosome Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to fo ...
s decreasing the effect of a termination codon. It's believed that nonsense suppressors keep a low concentration in the cell and do not disrupt normal
translation Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transl ...
most of the time. In addition, many genes do not have only one termination codon, and cells commonly use ochre codons as the termination signal, whose nonsense suppressors are usually inefficient. Nonsense suppressors are a useful genetic tool, but can also result in problematic side effects, since all identical stop codons in the genome will also be suppressed to the same degree. Genes with different or multiple stop codons will be unaffected. SUP35, a nonsense suppressor identified by Wickner in 1994, is a
prion protein Major prion protein (PrP), is encoded in the human by the ''PRNP'' gene also known as CD230 (cluster of differentiation 230). Expression of the protein is most predominant in the nervous system but occurs in many other tissues throughout the bod ...
. In synthetic biology, artificial suppressor elongator tRNAs are used to incorporate unnatural amino acids at nonsense codons placed in the coding sequence of a gene. Start codons can also be suppressed with suppressor initiator tRNAs, such as the amber stop codon suppressor tRNAfMet2(CUA). The amber initiator tRNA is charged with methionine and glutamine.


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