Phase Separation in PML Nuclear Bodies through a Multivalent PolySUMO-2/3 Network is required for Efficient DNA Recombination and Repair

Membrane-less organelles in the nucleus of mammalian cells have been suggested recently to assemble and function via LLPS mechanisms. One main driver of LLPS at PML NBs appears to be multivalent interaction between polySUMO chains and polySIM-containing proteins. We set out to analyze phase separation features within PML bodies using computer modeling, super-resolution and biochemical approaches. Functional aspects of LLPS at PML bodies will be analyzed during DNA recombination at PML-associated telomeres and/or DNA double-strand breaks.

Current State of Research

Using SRSim software for spatial and rule-based modeling of biochemical reaction systems we have established the simulation and visualization of the biogenesis of mature PML bodies from their component parts. The in silico analysis of PML body structure delivered a 3-dimensional model at molecular resolution revealing the spatial arrangements between PML’s poly-SUMO chains (scaffold) and SIM-containing partner proteins (clients). Multicolor super-resolution imaging was established to test in silico predictions of PML NB structure after cellular stress. In live cells fusion and fission events as well as rapid exchange of scaffold components and SIM-containing clients at PML NBs. Our data strongly support a model of polySUMO/polySIM-driven LLPS at PML NBs.