RT Journal Article
SR Electronic
T1 Clusters of bacterial RNA polymerase are biomolecular condensates that assemble through liquid-liquid phase separation
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2020.03.16.994491
DO 10.1101/2020.03.16.994491
A1 A-M Ladouceur
A1 B Parmar
A1 S Biedzinski
A1 J Wall
A1 SG Tope
A1 D Cohn
A1 A Kim
A1 N Soubry
A1 R Reyes-Lamothe
A1 SC Weber
YR 2020
UL http://biorxiv.org/content/early/2020/03/18/2020.03.16.994491.abstract
AB Once described as mere “bags of enzymes”, bacterial cells are in fact highly organized, with many macromolecules exhibiting non-uniform localization patterns. Yet the physical and biochemical mechanisms that govern this spatial heterogeneity remain largely unknown. Here, we identify liquid-liquid phase separation (LLPS) as a mechanism for organizing clusters of RNA polymerase (RNAP) in E. coli. Using fluorescence imaging, we show that RNAP quickly transitions from a dispersed to clustered localization pattern as cells enter log phase in nutrient-rich media. RNAP clusters are sensitive to hexanediol, a chemical that dissolves liquid-like compartments in eukaryotic cells. In addition, we find that the transcription antitermination factor NusA forms droplets in vitro and in vivo, suggesting that it may nucleate RNAP clusters. Finally, we use single-molecule tracking to characterize the dynamics of cluster components. Our results indicate that RNAP and NusA molecules move inside clusters, with mobilities faster than a DNA locus but slower than bulk diffusion through the nucleoid. We conclude that RNAP clusters are biomolecular condensates that assemble through LLPS. This work provides direct evidence for LLPS in bacteria and suggests that this process serves as a universal mechanism for intracellular organization across the tree of life.Significance Bacterial cells are small and were long thought to have little to no internal structure. However, advances in microscopy have revealed that bacteria do indeed contain subcellular compartments. But how these compartments form has remained a mystery. Recent progress in larger, more complex eukaryotic cells has identified a novel mechanism for intracellular organization known as liquid-liquid phase separation. This process causes certain types of molecules to concentrate within distinct compartments inside the cell. Here, we demonstrate that the same process also occurs in bacteria. This work, together with a growing body of literature, suggests that liquid-liquid phase separation is a universal mechanism for intracellular organization that extends across the tree of life.