**4. Conclusion**

In all living organisms HR is strictly regulated in time and in space to maintain the stability of the genome. Rad51 is the central protein in the HR process. The regulation of HR involves many protein interactions (Fig. 4) which are strongly dependent on posttranslational modifications. Indeed, almost all key mediator proteins of HR are subject to phosphorylation by specific kinases, thereby modulating some stage of this process (e.g. the nucleofilament formation). Hence, these posttranslational reactions underline the complexity of the regulation of HR. Despite of the several studies on the mechanism of Rad51 phosphorylation, its biochemical role in the HR reaction remains unclear.

The impact of phosphorylation on the interactions of Rad51 with its partners still needs to be determined. In order to better understand the regulation of HR, the future challenge will be to identify the complete interaction network of Rad51, the motor protein of HR.
