Transcription-Dependent Formation of Nuclear Granules Containing FUS and RNA Pol II.

Purified recombinant FUsed in Sarcoma (FUS) assembles into an oligomeric state in an RNA-dependent manner to form large condensates. FUS condensates bind and concentrate the C-terminal domain of RNA polymerase II (RNA Pol II). We asked whether a granule in cells contained FUS and RNA Pol II as suggested by the binding of FUS condensates to the polymerase. We developed cross-linking protocols to recover protein particles containing FUS from cells and separated them by size exclusion chromatography. We found a significant fraction of RNA Pol II in large granules containing FUS with diameters of >50 nm or twice that of the RNA Pol II holoenzyme. Inhibition of transcription prevented the polymerase from associating with the granules. Altogether, we found physical evidence of granules containing FUS and RNA Pol II in cells that possess properties comparable to those of in vitro FUS condensates.