Long multiply marked DNA repair template reveals lengths and fidelity of genome editing tracts in Schizosaccharomyces pombe

To test the ability of a fission yeast CRISPR-Cas9 system ( <i>SpEDIT</i> ) to carry out genome editing over distance, we constructed a 1,935 bp-long, dsDNA repair template that contained 45 base pair substitutions (SNPs), relative to the wild-type target locus <i>ade6</i> . Template-directed repair was efficient in the vicinity of the recombination-initiating dsDNA break, but the efficiency fell rapidly with distance (median editing tract length of 163 bp). The regularly distributed markers also revealed evidence for heteroduplex DNA at the ends of repair tracks and, unexpectedly, that DNA ends of the repair template participate in many (~18%) of the genome editing events.