In the past, many macromolecular complexes could not be structurally characterized at atomic resolution as they were unsuitable for crystallization and X-ray crystallography and as electron microscopy could not provide high resolution data. This changed rapidly in the last decade, as tremendous progress was achieved in the single particle cryo electron microscopy (cryo-EM) field. Meanwhile, cryo-EM became the method of choice to determine the structure of such complexes, opening a new era of structural biology. In this BAG we will, using cryo-EM, determine the structures of complicated protein machineries including large multi-subunit complexes, protein-nucleic acid complexes and membrane protein complexes. Our projects will contribute to improve the understanding of the molecular basis of energy conversion and cellular respiration, nitrate and ammonium metabolism, ribosome and ribosome-associated functions, DNA damage repair and maintenance.