Fig. 3: Mechanism of CRISPR prime editing for precise genome modification.
From: CRISPR-based functional genomics tools in vertebrate models

a Prime editing begins with Cas9 nickase fused to a RT and guided by a pegRNA. Cas9 nicks the target DNA strand, allowing RT to access the DNA for editing. b The pegRNA contains three components: a PBS, a RT template and an intended edit sequence. The nicked DNA strand anneals to the PBS, allowing reverse transcription of the edit. c A 3′ flap containing the desired edit is synthesized from the RT template, generating a new DNA segment with the desired sequence. d A competing 5′ unedited flap forms from the original DNA strand. The resolution of this heteroduplex determines which sequence is retained. e The edited strand is integrated into the genome, displacing the original noncomplementary strand. f DNA repair mechanisms synthesize the complementary strand to match the edited sequence, completing the prime editing process with a permanent and precise edit. (Figure created using Biorender.com).