In cells, a vast amount of DNA damage occurs from UV radiation, various chemical reagents, and errors during DNA replication and genetic recombination. These DNA damages are very harmful, and can result in mutagenesis and even in cell death. To remove these lesions, cells have various types of DNA repair systems, and most of them are common to many organisms, including human. Through the structural and functional analyses as well as basic research for cell imaging, this research team aims to understand the cellular systems of DNA repair systems in an extremely thermophilic model organism, Thermus thermophilus HB8. This team will address the development of single-molecule and whole-cell imaging?technologies, by using the SPring-8 beamline and XFEL, in collaboration with the other two teams in this group and with other research groups. The other methodologies used for imaging are (1) electron microscopy, especially electron tomography for in vivo cell imaging, (2) probe microscopy, which includes atomic force microscopy at video rate, for in vitro imaging, and (3) confocal laser scanning microscopy for in vivo cell imaging of target molecules tagged with thermophilic fluorescent protein domains (super folder GFP, YFP, etc.). These fluorescently-tagged protein domains are also used for in vitro imaging of the target molecules. In addition, as single-molecule imaging analyses, we will attempt to visualize protein-DNA interactions at high resolution. We have started with DNA repair systems as a model, because about 10 proteins involved in this system, which show very high affinity to damaged DNA, have been obtained. Since the proteins from T. thermophilus are stable in a vacuum, we can develop a technology to place a protein molecule onto a DNA molecule in a vacuum. This technology will contribute to single-molecule imaging in the future with XFEL. The cell-wall syntheshis system is also the target for cell imaging.