Reversions and suppression Flashcards
What is a reversion?
A mutant regains the WT phenotype. Can be spontaneous or induced
What is a revertant?
The organism that underwent a reversion
What are the two types of mutations that can cause reversions?
True reversion and suppression
What is true reversion?
A back mutation that becomes changed back to the original gene sequence
What is a suppressor?
A second mutation at a different site that restores the original phenotype
Why is a suppressor mutation only considered a pseudo-reversion?
The original mutation is still there, you just don’t see it
Are suppressions or true reversions more common?
Suppressions
What is the reversion frequency?
Frequency of cells in a population that have reverted to a WT phenotype
RF = # of revertants/# of total mutant bacteria
Between a base pair substitution, frameshift, and deletion, which is the most likely to revert? Which is the least likely?
Frameshifts are the most likely because they tend to have in repetitive mutation hotspots
Deletions can never revert
What is intragenic suppression?
The second mutation that suppresses the first one is in the same gene as the original
What is a same site reversion?
The suppressor mutation happens at the same AA position in the protein
What is second site reversion?
The suppressor happens at another codon that encoding an AA that interacts with the first one
What has to happen with a second site suppressor mutation if it was to revert the original mutation?
It has to restore the interaction that was lost with the original mutation
How can intragenic suppressor mutations cause frameshifts to revert?
Get a second frameshift mutation downstream of the original mutation
What will determine if an intragenic frameshift suppressor can actually revert the original frameshift?
The area between the two mutations will still be wrong, so that area can’t be too long or be in a region essential to function
What are the 5 types of intergenic suppressor mutations?
Interaction suppresors Overproduction suppressors Informational suppressors Dosage suppressors Bypass suppressors
How does an interaction suppressor cause reversion?
It mutates the interaction site in a second protein that interacts with the first mutant protein so that it restores the interaction that was lost
What is intergenic suppression?
The suppressor mutation is in a different gene than the original one
What is overproduction suppression?
The suppressor mutation overcomes the effects of the original mutation by overproducing the mutant protein
Why doesn’t an overproduction suppressor work for every mutant protein?
Only works if the original mutation just reduced function and didn’t knock it out
What are 2 places that an overproduction suppressor mutation can affect?
Regulatory sites that result in an upregulation of the mutant protein
Stability or degradation of mutant protein
What are bypass suppressors?
The suppressor mutations turns on an alternative pathway that bypasses the original mutation. Really common
What are dosage suppressors?
Suppressor mutation stabilizes a mutant protein that got destabilized by the original mutation by increasing the concentration of a stabilizing factor like a protein chaperone
What kind of original mutation do dosage suppressors suppress?
Mutations that destabilize the protein
