= Suppressor mutation
A <suppressor mutation> is a second genetic change that reduces or counteracts a specified effect of another change. The resulting <phenotype> can move toward the original functional state while the original altered <DNA> sequence remains present. Suppression can act through another position in the same <gene> or through a different gene; recovery of one readout need not restore every property of the organism.
A constructed <reading frame> example makes the distinction visible. A one-<nucleotide> insertion changes the downstream grouping of <codons>. A second, later one-<nucleotide> deletion can restore the original grouping after the second change, because the net length change is $1-1=0$. The sequence between the two changes can still specify different <amino acids>. Two additional inserted nucleotides would likewise give a net change of three, restoring phase downstream without recreating the original <nucleotide sequence>. Whether function recovers remains an experimental question.
Suppressor screens also identify mutations that bypass a defined regulatory phenotype. In a 2002 <SecM> study, mutations in <23S ribosomal RNA> and <ribosomal protein L22> relieved <ribosome stalling>. The affected positions faced the <ribosomal exit tunnel> constriction, linking the altered response to the environment around the nascent <polypeptide>.<The ribosomal exit tunnel functions as a discriminating gate by Hitoshi Nakatogawa and Koreaki Ito>[Abstract, arrest-bypass mutations and tunnel-facing residues]{ref} Such a screen finds a functional relationship; by itself it does not prove that every suppressor physically contacts the original altered component.
Back to article page
