Reversions and suppression

Question 1

What is a reversion?

Answer 1

A mutant regains the WT phenotype. Can be spontaneous or induced

Question 2

What is a revertant?

Answer 2

The organism that underwent a reversion

Question 3

What are the two types of mutations that can cause reversions?

Answer 3

True reversion and suppression

Question 4

What is true reversion?

Answer 4

A back mutation that becomes changed back to the original gene sequence

Question 5

What is a suppressor?

Answer 5

A second mutation at a different site that restores the original phenotype

Question 6

Why is a suppressor mutation only considered a pseudo-reversion?

Answer 6

The original mutation is still there, you just don’t see it

Question 7

Are suppressions or true reversions more common?

Answer 7

Suppressions

Question 8

What is the reversion frequency?

Answer 8

Frequency of cells in a population that have reverted to a WT phenotype
RF = # of revertants/# of total mutant bacteria

Question 9

Between a base pair substitution, frameshift, and deletion, which is the most likely to revert? Which is the least likely?

Answer 9

Frameshifts are the most likely because they tend to have in repetitive mutation hotspots
Deletions can never revert

Question 10

What is intragenic suppression?

Answer 10

The second mutation that suppresses the first one is in the same gene as the original

Question 11

What is a same site reversion?

Answer 11

The suppressor mutation happens at the same AA position in the protein

Question 12

What is second site reversion?

Answer 12

The suppressor happens at another codon that encoding an AA that interacts with the first one

Question 13

What has to happen with a second site suppressor mutation if it was to revert the original mutation?

Answer 13

It has to restore the interaction that was lost with the original mutation

Question 14

How can intragenic suppressor mutations cause frameshifts to revert?

Answer 14

Get a second frameshift mutation downstream of the original mutation

Question 15

What will determine if an intragenic frameshift suppressor can actually revert the original frameshift?

Answer 15

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

Question 16

What are the 5 types of intergenic suppressor mutations?

Answer 16

Interaction suppresors
Overproduction suppressors 
Informational suppressors
Dosage suppressors 
Bypass suppressors

Question 17

How does an interaction suppressor cause reversion?

Answer 17

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

Question 18

What is intergenic suppression?

Answer 18

The suppressor mutation is in a different gene than the original one

Question 19

What is overproduction suppression?

Answer 19

The suppressor mutation overcomes the effects of the original mutation by overproducing the mutant protein

Question 20

Why doesn’t an overproduction suppressor work for every mutant protein?

Answer 20

Only works if the original mutation just reduced function and didn’t knock it out

Question 21

What are 2 places that an overproduction suppressor mutation can affect?

Answer 21

Regulatory sites that result in an upregulation of the mutant protein
Stability or degradation of mutant protein

Question 22

What are bypass suppressors?

Answer 22

The suppressor mutations turns on an alternative pathway that bypasses the original mutation. Really common

Question 23

What are dosage suppressors?

Answer 23

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

Question 24

What kind of original mutation do dosage suppressors suppress?

Answer 24

Mutations that destabilize the protein

Question 25

What are informational suppressors?

Answer 25

A suppressor mutation that is in the translation machinery and causes the original mutation to be misread to get a functional protein from a mutant gene

Question 26

Where are informational suppressor mutations found?

Answer 26

Translation machinery like tRNAs