Base editing

Question 1

What does the base editing primarily address?

Answer 1

Transition point mutation

Base editors install or correct the four most common types of point mutations at target DNA sites without her requiring DSBs or donor DNA templates

Question 2

Cytosine base editor (CBE)

Answer 2

C—>T
G—>A

Question 3

Adenine base editor (ABE)

Answer 3

A—>G
T—>C

Question 4

Components of the cytosine base editors

Answer 4

See pic

1. SgRNA: single guide RNA
2. Nickase (re-engineered cas9 that does not make DSBs)
3. SsDNA specific cytidine deaminase
4. UGI: protects the Uracil from removal by the cell

Question 5

Process of base editing

Answer 5

1. Nickase recognize PAM sequence and open up the DNA
2. SgRNA bind to one of the DNA strands
3. Deamination of the target C in ssDNA
4. Nickase nicks the non-edited strand to stimulate the DNA repair mechanism to change the G on the non-edited strand to A
5. Mismatch repair the non-edited strand to A
6. Permanent change of the pair from G/C to A/T

Question 6

Limitation

Answer 6

It edits the Base (such as Cytosine) within 5 base window. Ie, if there are more than one Cytosine bases within that 5 base window, they will all be edited even if they are off-target

Limited to only transition point mutation (ie one purine to another, one pyrimidine to another)

Question 7

How do CDEs work?

Answer 7

See pic

Question 8

How do ABEs work?

Answer 8

See pic