Talk:CH391L/S2013 Tanya Raymond Jan 23 2013

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  • Logan Myler In the model that the authors propose, CtIP and Exo1 are responsible for parallel pathways to initially resect back the DNA, and this is followed by a phosphorylation-dependent loading of DNA2 and CtIP for further resection. However, in the absence of CtIP, there is still RPA loading onto chromatin, and in the absence of DNA2, RPA loading is almost completely abrogated. Isn't this contradictory to the model?
    • Tanya Raymond Yes. The authors describe a model in which resection, initiated by either Exo1 or CtIP, occurs and long range resection is performed primarily by DNA2. This is their logic for why, even, in the presence of active Exo1, DNA2 causes near total abrogation of resection upon CtIP deletion. But their model is counter-intuitive in another regard since, according to their model, CtIP may initiate resection which causes recruitment of ATR via RPA binding. ATR then phosphorylates CtIP which is essential for long range resection and loading to chromatin. Previously, CtIP has primarily been associated with the initiation of resection and limited processing of DNA ends, and this recruitment to chromatin after phosphorylation and the effect on long range resection has not been observed (to my knowledge). [1] That said, what one would ideally like to investigate in order to make these details clearer is to look at these interactions and the effect of p-CtIP on resection in an in vitro experiment.

1. Neale, M.J., Pan, J., and Keeney, S. (2005). Endonucleolytic processing of covalent protein-linked DNA double-strand breaks. Nature 436, 1053–1057

    • Tanya Raymond By "in vitro" I mean to say using purified recombinant proteins.