Resolution of D-loop Structures through Holliday Junction Intermediates

A D-loop can be cleaved by the complex of MUS81 and EME1 (MUS81:EME1) or MUS81 and EME2 (MUS81:EME2) and resolved without the formation of double Holliday junctions, generating cross-over products. All steps involved in this process have not been elucidated.

Alternatively, double Holliday junctions can be created by ligation of crossed-strand intermediates. Double Holliday junctions can then be resolved through the action of the BLM helicase complex known as BTRR (BLM:TOP3A:RMI1:RMI2). BLM-mediated resolution of Holliday junction intermediates prevents sister chromatid exchange (SCE) between mitotic chromosomes and generates non-crossover products. SPIDR enables recruitment of the BTTR complex to the ionizing radiation-induced foci. The complex of FIGNL1 and FIRRM, which, through FIGNL1, simultaneously interacts with SPIDR and RAD51, may facilitate the function of SPIDR in promoting the no cross-over route of homologous recombination repair. Mitotic SCE can result in the loss-of-heterozygosity (LOH), which can make the cell homozygous for deleterious recessive mutations (e.g. in tumor suppressor genes). Double Holliday junctions can also be resolved by cleavage, mediated by GEN1 or the SLX-MUS complex (composed of SLX1A:SLX4 heterodimer and a heterodimer of MUS81 and EME1 or, possibly, EME2). The resolvase activity of GEN1 and SLX-MUS predominantly results in crossover products, with SCE.