Donor transgenic construct for use in the homology assisted CRISPR knock-in (HACK) method. Designed to convert a GAL4 line to a Cas9 line in vivo. The construct contains DNA that will be incorporated into the genome (in this case 2A-Cas9 plus an excisable loxP cassette containing a Rnor\Cd2^{miRNA-6.lexAop} gene) flanked by 5' and 3' homology arms to the targeted sequence (in this case GAL4). It also contains a gRNA that targets GAL4. The Rnor\Cd2^{miRNA-6.lexAop} gene (along with other components present in the original donor construct) allow for lethality-based selection to enrich for correctly targeted events (provided that a source of lexA driver expression is also provided). CRISPR/Cas9 is used to induce a double-strand DNA break in the target GAL4 sequence, which is then repaired via homology-directed repair using the donor as a template, resulting in insertion of both 2A-Cas9 and the excisable Rnor\Cd2^{miRNA-6.lexAop}-containing loxP cassette into the GAL4 sequence. The 'self-cleaving' 2A peptide will release Cas9 and and nonfunctional GAL4 as two separate proteins after translation of the transcript that is produced by the converted transgene.