Despite its increased efficacy, the edit inserted by PE2 might still be removed due to DNA mismatch repair of the edited strand. To avoid this problem during DNA heteroduplex resolution, an additional single guide RNA (sgRNA) is introduced. This sgRNA is designed to match the edited sequence introduced by the pegRNA, but not the original allele. It directs the Cas9 nickase portion of the fusion protein to nick the unedited strand at a nearby site, opposite to the original nick. Nicking the non-edited strand causes the cell's natural repair system to copy the information in the edited strand to the complementary strand, permanently installing the edit. However, there are drawbacks to this system as nicking the unaltered strand can lead to additional undesired indels.