Dynamics of double-strand break repair


In a new paper in the journal Genetics, former Brandeis postdoc Eric Coïc and undergrads Taehyun Ryu and Sue Yen Tay from Professor of Biology Jim Haber’s lab, along with grad student Joshua Martin and Professor of Physics Jané Kondev, tackle the problem of understanding the dynamics of homologous recombination after double strand breaks in yeast. According to Haber,

The accurate repair of chromosome breaks is an essential process that prevents cells from undergoing gross chromosomal rearrangements that are the hallmark of most cancer cells.  We know a lot about how such breaks are repaired.  The ends of the break are resected and provide a platform for the assembly of many copies of the key recombination protein, Rad51.  Somehow the Rad51 filament is then able to facilitate a search of the entire DNA of the nucleus to locate identical or nearly identical (homologous) sequences so that the broken end can pair up with this template and initiate local copying of this segment to patch up the chromosome break.  How this search takes place remains poorly understood.

The switching of budding yeast mating type genes has been a valuable model system in which to study the molecular events of broken chromosome repair, in real time.  It is possible to induce synchronously a site-specific double-strand break (DSB) on one chromosome, within the mating-type (MAT) locus.  At opposite ends of the same chromosome are two competing donor sequences with which the broken ends of the MAT sequence can pair up and copy new mating-type sequences into the MAT locus.

Normally one of these donors is used 9 times more often than the other.  We asked if this preference was irrevocable or if the bias could be changed by making the “wrong” donor more attractive – in this case by adding more sequences to that donor so that it shared more and more homology with the broken ends at MAT.  We found that the competition could indeed be changed and that adding more homologous sequences to the poorly-used donor increased its use.


In collaboration with Jané Kondev’s lab we devised both a “toy” model and a more rigorous thermodynamic model to explain these results.  They suggest that the Rad51 filament carrying the broken end of the MAT locus collides on average 4 times before with the preferred donor region before it actually succeeds in carrying out the next steps in the process that lead to repair and MAT switching.

Dynamics of homology searching during gene conversion in Saccharomyces cerevisiae revealed by donor competition Eric Coïc , Joshua Martin, Taehyun Ryu, Sue Yen Tay, Jané Kondev and James E. Haber. Genetics. 2011 Sep 27 2011 Sep 27

Keith Cheveralls ’09, Daniel Beller ’10, and Netta Engelhardt ’11 awarded NSF Graduate Research Fellowships

Former physics majors Keith Cheveralls ’09 and Daniel Beller ’10 and current physics major Netta Engelhardt ’11 have been awarded the prestigious National Science Foundation Graduate Research Fellowship. The fellowship recognizes and supports outstanding graduate students in the US who have demonstrated exceptional promise in science research. Keith is currently a first year graduate student at UC Berkeley; while at Brandeis he did his senior thesis with Professor Jane Kondev and was a co-author on a paper that appeared last year in the Proceedings of the National Academy of Sciences. Dan, a first year graduate student at the University of Pennsylvania, completed his senior thesis at Brandeis with Professor Zvonimir Dogic and Professor Robert Meyer.  Currently, Dan is conducting research on liquid crystals in the group of Professor Randall Kamien at UPenn. Netta is currently doing her senior thesis with Professor Matthew Headrick, and is planning to attend graduate school in physics next year.

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