CRISPR 101: Cytosine and Adenine Base Editors

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Diagram of the Cascade complex with gRNA bound to target DNA, after recruitment of Cas3. Cas3 is about to nick the non-target strand.
Graphic showing the workflow of using a pooled AAV CRISPR library in vitro. Step A shows the AAV containing the library with either the gRNA only or gRNA plus Cas9 and infecting cells expressing Cas9 or wild-type. The different guides are represented by different colors in individual cells. Step B shows the results of the positive or negative selection, with only one type of guide (color) being chosen. Step C shows verification using next generation sequencing.
A cartoon of a prime editor with two different edit sequences. The DNA sequences are shown with one strand edited and a 5′ DNA flap, before heteroduplex resolution and DNA repair.  The first edit has an unchanged PAM. This DNA is shown connected to the prime editor by a two-way arrow, indicating that the editor can re-bind. Re-nicking is represented by scissors and would remove the newly edited DNA.  The second edit has an altered PAM. A one-way arrow leads from the prime editor to this edit, indicating that the changed PAM prevents the editor from re-binding.
A cartoon overlayed on several crystal structures showing the parts of the prime editor: the Cas9 nickase domain, the reverse transcriptase domain, and the pegRNA.
Alt text: A schematic illustration of the CRISPR/Cas9-based approaches mentioned above. The first illustration (A) shows a DSB made at a transcription start site upstream of an exon. The second illustration (B) shows a DSB made at splice sites. The third illustration (C) shows a DSB made upstream and downstream of an exon to fully remove a genomic fragment. The fourth illustration (D) shows a DSB made within an exon to insert a synthetic polyadenylation signal. 
CRISPR prime editing schematic.
Schematic of Fragmid assembly process from day one to day four and resulting vector architecture.  On day one fragment plasmids plus a destination vector are assembled using Golden Gate (BbsI). On day two the assembled vector containing a Guide (2xBsmBI), Promoter, N-terminus, Cas protein, C’terminus, and 2A-Selection undergoes an exonuclease V cleanup followed by transformation and plating. On day three two colonies per construct are picked, miniprepped and restriction digested for gel validation/whole plasmid sequencing. Below the assembled vector are examples of six vector architectures including pRDA_512 lentivirus, pRDA_722 lentivirus, pRDA_789 CROPseq lentivirus, pRDA_889 AAV, pRDA_575 Piggyback, and pRDA_791 empty plasmid.

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