CRISPR-Cas9 base editing differs from standard CRISPR-Cas9 nuclease in that base editors:
- A Create double-strand breaks at two loci simultaneously to excise large genomic segments
- B Use catalytically dead Cas9 (dCas9) fused to a deaminase to chemically convert one base to another without creating double-strand breaks ✓
- C Introduce HDR templates more efficiently by fusing Cas9 to a RAD51 recombinase
- D Deliver base corrections epigenetically without altering the DNA sequence
Explanation
Base editors consist of a catalytically impaired Cas9 (nickase or dCas9) fused to a DNA base-modifying enzyme (deaminase). Two main classes exist: cytosine base editors (CBE) use cytidine deaminase to convert C→U (which is read as T), enabling C•G to T•A transitions; adenine base editors (ABE) use an engineered adenosine deaminase to convert A→I (inosine, read as G), enabling A•T to G•C transitions. Because base editors do not create double-strand breaks, they avoid the error-prone NHEJ pathway and associated indels/large deletions. This makes them more precise for point mutation correction (e.g., correcting sickle cell Glu6Val mutation or correcting PCSK9 gain-of-function). Prime editing is a further evolution using a reverse transcriptase-Cas9 fusion.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.