Provided herein are polynucleotides, vectors, complexes, compositions, systems, kits, methods and uses for enriching for
gene editing in a
cell. Some aspects of the disclosure relate to the use of a
polynucleotide cassette comprising a coding sequence of a selection
marker gene that is disrupted by a synthetic
intron sequence to prevent
gene expression of the selection marker. The synthetic
intron further comprises a defective splice site that is correctable by a base edit such that when the splice site is corrected by a
gene editor, the
intron is removed by the endogenous
slicing system of the
cell and expression of the selection
marker gene can occur. Methods described herein screen for the presence of active gene editors within the
cell by subjecting the cell to the selection pressure of the selection marker.