DNA-end processing

In human cells, exogenous and endogenous DNA damaging agents as well as programmed DNA re-arrangements lead to the formation of millions of double-stranded DNA breaks (DSBs) in our bodies every few minutes. Fortunately, cells possess robust mechanisms to repair DNA breaks. One such DNA repair mechanism that is present in all domains of life is homologous recombination, where the sister chromatid is used as a template for faithful repair.

Failure to properly repair DNA damage has devastating consequences, resulting in loss of chromosome structural integrity and genomic instability that is associated with developmental defects, deficiencies of the immune system and cancer predisposition.

Recombinational repair of DSBs is a complex, multistep process orchestrated by a collection of protein machines. It is initiated by the long-range resection of the DNA end to form a 3´-terminated ssDNA overhang. This is a substrate for the RecA/RAD51 recombinase that catalyses strand exchange; the next step of the repair pathway. If the initial structure of the DSB is not a simple blunt ended duplex, as is thought to be the case for those generated by replication fork collapse, ionizing radiation or programmed cleavage during meiosis, then long-range resection may be preceded by a pre-processing step in which this “complex” DSB structure is trimmed to generate a simple DNA end. All of these end processing reactions are catalysed by a team of helicases and nucleases that act together to unwind and degrade the DNA from the site of the DSB.

In bacterial cells, our work and that of others has led to an exquisitely detailed understanding of the long range resection step that is catalyzed by AddAB or RecBCD-type helicase-nucleases in a manner regulated by Chi recombination hotspots.

Topic-related papers of the group

Gilhooly et al. Nucleic Acids Research 44(6), 2727-2741 Published Online Jan 13 (2016). Chi hotspots trigger a conformational change in the helicase-like domain of AddAB to activate homologous recombination. LINK

 Carrasco et al. DNA Repair 20, 119-129 (2014) (cover article). Single molecule approaches to monitor the recognition and resection of double-stranded DNA breaks during homologous recombination. LINK

Carrasco et al. PNAS 110 (28), E2562-2571 (2013). On the mechanism of recombination hotspot scanning during double-stranded DNA break resection. LINK

Yeeles et al. Molecular Cell 42, 806-816 (2011). Recombination Hotspots and Single-Stranded DNA Binding Proteins Couple DNA Translocation to DNA Unwinding by the AddAB Helicase-Nuclease. LINK

Collaborators

University of Bristol: Mark Dillingham Group