The large ribosomal subunit is responsible for peptide bond formation. Compared with the small subunit, three ribosomal RNAs are incorporated into the mature particle. We have studied the early nucleolar assembly of the large ribosomal subunit by cryo-EM to show that a modular assembly pathway is employed for the formation of this particle (Sanghai et al. 2018). The structure of this assembly intermediate has shed light on the early formation of the polypeptide exit tunnel and other key aspects of large subunit maturation. Ongoing research in the lab is aimed at how this particle transitions from the nucleolus to the cytoplasm.