Researchers working at the Institut Pasteur in Montevideo (member of the Institut Pasteur International Network), in collaboration with the Uruguayan Medical School, obtained for the first time ever high-resolution images of the Bovine Leukemia Virus (BLV) capsid protein. Their images reveal unprecedented elements of flexibility in this protein, which are key for the assembly of the infectious particle. These findings, reported today in Science, represent a major progress in understanding retrovirus biology, opening new avenues towards the development of antiretroviral therapies.