CORDIS

Structure-specific endonucleases are essential for the processing of secondary DNA structures and preventing genomic instability. However, because these enzymes cleave the DNA double helix, they can be viewed as double edge swords. Indeed, unless properly controlled structure-specific endonucleases may in some cases lead to, rather than prevent, chromosome instability and ultimately tumourigenesis. Therefore, complex control mechanisms must exist to ensure a proper coordination and usage of multiple structure-specific endonucleases in the cell.

Our research focuses on understanding how structure-specific endonucleases are controlled. For this we have been combining studies on these enzymes in fission yeast, a powerful model system to investigate genome maintenance mechanisms, and in human cells. We have established to key findings during the course of this project:

1) We have unravelled a novel mode of regulation of the Mus81-Eme1 structure-specific endonuclease in fission yeast. Mus81-Eme1 is required to process DNA structures, such as Holliday junctions, that covalently link chromosomes and which, if left unresolved, will prevent the proper segregation of chromosomes into to the daughter cells. We have found that Eme1 is phosphorylated in a Rad3-dependend manner and that, although this is not required in the general response to gentoxic drugs, it is critical for preventing spontaneous genome instability in absence of the Rqh1 helicase.

2) We have identified and characterised the human ortholog of the yeast Slx4 protein. We show that SLX4 is a subunit of a Holliday junction resolvase that interacts with multiple DNA repair/recombination endonucleases. We propose that SLX4 acts as a coordination and control unit for structure-specific endonucleases in human cells and that it has pivotal functions in several genome maintenance mechanisms. Considering the marked spontaneous and drug induced phenotypes associates with depletion of SLX4 in human cells and the variety of DNA repair/recombination pathways it appears to be involved in, we believe that the identification of human SLX4 opens new avenues for understanding the processes involved in the maintenance of genome stability and the prevention of the onset of cancer and other human diseases.