The dark side of circular RNA, a new driver of genome instability

Circular RNAs (circRNAs) are covalently closed RNA molecules whose functions are still largely uncharacter-ized. In the July issue of Cancer Cell, Conn et al.(1) demonstrate that circRNA can bind cognate DNA loci, form-ing circRNA-DNA hybrids (circR loops), driving genetic rearrangements of MLL/KMT2A, which are associated with the most aggressive acute leukemias.