DNA repair

DNA repair

DNA double stranded breaks (DSBs) pose a serious threat to genome integrity. Homologous recombination (HR) (see figure) repairs DSBs by exchanging nucleotides between identical or closely related DNA molecules. DSB-repair is a highly conserved process using similar mechanisms from yeast to man. Hence, it is possible to use model organisms to study DSB-repair and draw conclusions that are relevant for humans. Since mutations that impair DSB-repair in humans can be detrimental and cause cancer it is important to study DSB-repair. Because yeast is an excellent genetic model organism we study HR in Saccharomyces cerevisiae or Baker’s yeast.

 

Schematic picture of the DSBR and SDSA-pathways for DSB repair. The severed chromatid is shown in blue and the intact template is shown in red.

 

We explore the resolution of Holliday junctions (HJs), which are central intermediates during HR. The Yen1 and Mus81 nucleases from yeast can cleave replication forks and HJs in vitro. In addition a complex containing the Sgs1 helicase and a topoisomerase (Top3) can dissolve HJs. However, the cellular function of Yen1/Mus81/Top3 is not completely known motivating an extensive characterization of these molecules both biochemically and genetically.

As an example, we have discovered that Yen1 is modified by the Small Ubiquitin related modifier (SUMO). Furthermore, the SUMOylation of Yen1 promotes a molecular interaction with a poorly characterized helicase/ubiquitin-ligase. We are currently exploring this and other observations to obtain a better understanding of how cells deal with branched DNA repair intermediates.

Links

Saccharomyces genome database – a comprehensive knowledge base of Baker’s yeast http://www.yeastgenome.org/

Genolevures a site for genomic exploration of other ascomycetes http://www.genolevures.org/

An excellent lecture on DNA repair/recombination
http://www.youtube.com/watch?v=UzXcq2h0VCk