RT Journal Article SR Electronic T1 nucGEMs probe the biophysical properties of the nucleoplasm JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.11.18.469159 DO 10.1101/2021.11.18.469159 A1 Tamás Szórádi A1 Tong Shu A1 Gururaj R. Kidiyoor A1 Ying Xie A1 Nora L. Herzog A1 Andrew Bazley A1 Martina Bonucci A1 Sarah Keegan A1 Shivanjali Saxena A1 Farida Ettefa A1 Gregory Brittingham A1 Joël Lemiere A1 David Fenyö A1 Fred Chang A1 Morgan Delarue A1 Liam J. Holt YR 2021 UL http://biorxiv.org/content/early/2021/11/20/2021.11.18.469159.abstract AB The cell interior is highly crowded and far from thermodynamic equilibrium. This environment can dramatically impact molecular motion and assembly, and therefore influence subcellular organization and biochemical reaction rates. These effects depend strongly on length-scale, with the least information available at the important mesoscale (10-100 nanometers), which corresponds to the size of crucial regulatory molecules such as RNA polymerase II. It has been challenging to study the mesoscale physical properties of the nucleoplasm because previous methods were labor-intensive and perturbative. Here, we report nuclear Genetically Encoded Multimeric nanoparticles (nucGEMs). Introduction of a single gene leads to continuous production and assembly of protein-based bright fluorescent nanoparticles of 40 nm diameter. We implemented nucGEMs in budding and fission yeasts and in mammalian cell lines. We found that the nucleus is more crowded than the cytosol at the mesoscale, that mitotic chromosome condensation ejects nucGEMs from the nucleus, and that nucGEMs are excluded from heterochromatin and the nucleolus. nucGEMs enable hundreds of nuclear rheology experiments per hour, and allow evolutionary comparison of the physical properties of the cytosol and nucleoplasm.Competing Interest StatementThe authors have declared no competing interest.