Oliver J Wilkinson, Alejandro Martin-Gonzalez, Hae Joo Kang, Sarah J Northall, Dale B Wigley, Fernando Moreno-Herrero and Mark S Dillingham.
The DNA of living cellular organism is subjected to changes and damages during a cells lyfe-cicle. Homologous recombination (HR) is one of the main cellular mechanisms for DNA damage-repair. It uses a homologous donor DNA as a template and thus is a potentially error-free repair mechanism. A key early factor in HR is CtIP. Little is known about this protein apart from its role in the initial steps of HR and its tetrameric oligomeric state in solution for a small part of the protein. Here we have studied the oligomeric state of human CtIP (hCtIP) and its interaction with DNA using Atomic Force Microscopy (AFM). AFM imaging of hCtIP shows five classes of particles classified according to their morphology and volume analysis. In addition, AFM images of CtIP-DNA binding reactions show the formation of long molecules as a consequence of association of shorter DNAs by CtIP acting as a bridge. Bridging events are dependent on [hCtIP] and on the oligomeric state of hCtIP, as corroborated with mutants. In this scientific research we propose that CtIP interacts directly with other proteins involved in DNA damage repair and signalling, and may therefore act as a platform to co-ordinate the repair of two-ended DNA breaks via HR.