Deinococcus radiodurans (DEIRA) is an extreme radiation and desiccation resistant bacterium, which tolerates radiation doses up to 5000 Grays without loss of viability. The mechanism of this outstanding resistance is not known, but is probably a result of efficient genome packing, cell structure and DNA repair. For ten years the fellow has studied structure/function relations of proteins in the Base Excision Repair (BER) pathway from DEIRA, in order to determine their role for the extreme radiation resistance. Results from crystal structures of six BER proteins show that they possess both catalytic and structural modifications which may improve the DNA repair efficiency and repertoire of this organism. The general idea is that double strand break (DSB) repair is most important for the ability of DEIRA to maintain its genome stability during exposure to ionising radiation. However, recent results show that BER proteins are important for prevention of DSB, and suggest that the BER pathway is more important for the radiation resistance of DEIRA than previously believed. This hypothesis will be tested by performing gene expression profiling (RT-PCR) of native strains and analysis of genome reassembly and viability of BER knock out strains, upon exposure to ionising radiation. The biological function of metal clusters in selected BER proteins will also be analysed by Electron Paramagnetic Resonance (EPR) and X-ray crystallography. The project will be hosted by Instituto de Technologia Química e Biológica (ITQB) at the Universidade Nova de Lisboa, Portugal, and will benefit immensely from the infrastructure and multidisciplinary expertise offered by this institute. The project will facilitate training within gene expression profiling, genetics (generation of knock out strains) and advanced metallo-enzyme analysis (EPR), and thus extend the fellows current toolbox for protein function and structure analysis which will enable her to obtain professional maturity.