Single particle electron cryomicroscopy (Cryo-EM) has become the method of choice for determining the structure of large macromolecular complexes and membrane proteins, which were previously particularly difficult to study using X-ray crystallography. In recent years, this method has also proved useful for the structure determination of smaller proteins such as GPCRs or transporters. In this BAG, we will use the state-of-the-art cryo-EM facility at ESRF to 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 a better understanding of essential cellular processes such as energy conversion and cellular respiration, nitrate and ammonium metabolism, ribosome and ribosome-associated functions, and DNA damage repair and maintenance mechanisms.