Ribosomes are ubiquitous macromolecular machines ensuring the translation of mRNA into proteins. Ribosomes are composed of a small and a large subunits, respectively termed 40S and 60S in eukaryotes. Assembly of those huge ribonucleoprotein complexes is a very complex and dynamic process, that requires more than 200 maturation factors interacting transiently with the forming particles. Ribosome biogenesis defects have recently been associated to an increasing list of human genetic diseases and cancers; understanding those diseases calls for a better knowledge of ribosome maturation pathways in human cells. 
Our group focuses on studying the mechanisms enabling the assembly of eukaryotic ribosomes, using both yeast and mammal cells as models. To do so, we notably use cryo-electron microscopy coupled to image analysis techniques to determine the 3D structures of pre-40S particles. Cryo-electron microscopy (cryo-EM) is a very powerful method that allows determination of the 3D structure of very large complexes. Structures of late pre-40S particles in yeast were solved to intermediate (~20 Å) resolution with this approach. 
We have already made use of cryo-EM and image analysis on the computing facilities of CalMIP to solve the first 3D structure of a pre-40S particle purified from human cells, to 19 Å resolution. This work has given rise to a first scientific article, currently under revision for the journal Nucleic Acids Research. 
We have acquired cryo-EM datasets of other pre-40S particles purified at other maturation steps, either from baker's yeast or human cells, that we would like to process using CalMIP's computational facilities. The various 3D reconstructions that we will obtain at the highest possible resolution should allow us to propose the first morphogenesis depiction of the assembly of the eukaryotic small ribosomal subunit.