Chromosome Preference During Homologous Recombination Repair of DNA Double-Strand Breaks in Drosophila melanogaster.

DNA double-strand breaks (DSBs) are especially toxic DNA lesions that, if left unrepaired, can lead to wide-ranging genomic instability. Of the pathways available to repair DSBs, the most accurate is homologous recombination (HR), where a homologous sequence is used as a donor template to restore genetic information at the break site. While much of the biochemical aspects of HR repair have been characterized, how the repair machinery locates and discriminates between potential homologous donor templates throughout the genome remains elusive. We use Drosophila melanogaster to investigate whether there is a preference between intrachromosomal and interhomolog donor sequences in mitotically dividing cells. Our results demonstrate that, although interhomolog HR is possible and frequent if another donor template is not available, intrachromosomal donor templates are highly preferred. This is true even if the interhomolog donor template is less diverged than the intrachromosomal donor template. Thus, despite the stringent requirements for homology, the chromosomal location of the donor template plays a more significant role in donor template choice.