Fig. 5.

Preventing the formation of “daisy necklaces.” (A) Any recombination event that moves a DNA template for guide RNA from one element to another, where it will be reliably copied, could create a daisy necklace capable of self-propagating drive. (B) Because promoters can be changed, repetition of the conserved DNA template sequence is a key problem. (C) Using existing data, we generated a template identifying candidate positions presumed tolerant of sequence changes. (D) Relative activities of candidate guide RNAs generated from the template were assayed by using a Cas9 transcriptional activator screen using a tdTomato reporter in human cells.