Fig. 6: PopZ material properties affect cytosol organization.
a PopZ IDR-156 condensates retain ribosome exclusion. (left) Slice through a tomogram of a cryo-focused ion beam-thinned ΔpopZ Caulobacter cell overexpressing mCherry-PopZ with IDR-156. (right) Segmentation of the tomogram in (left) showing annotated S-layer (orange), outer membrane (dark brown), inner membrane (light brown), and ribosomes (gold). Scale bar, 0.25 μm. b PopZ IDR-156 condensates retain DNA exclusion. PopZ IDR-156 condensates expressed in ΔPopZ cells dynamically moved in the cytosol and excluded DAPI-stained DNA (blue). Scale bar, 5 μm. c The CtrA activation network is sequestered to the PopZ condensate. The schematic shows the auto-kinase CckA92 phosphorylating the phospho-transfer protein, ChpT45, which in turn phosphorylates the master transcription factor, CtrA93. All three proteins are sequestered to the PopZ condensate26,29,30. Phosphorylation of CtrA occurs largely inside the condensate30. CtrA~P leaves the DNA-free PopZ condensate and activates an array of asymmetry regulating genes, including sciP94,95 and pilA96. d, e. PopZ material properties affect ChpT recruitment. d Representative cells are shown for pentavalent, IDR-40, and IDR-156. e The graph shows the partition coefficient of ChpT inside PopZ condensates as a function of condensate mobility. The coefficient was calculated as ChpT fluorescence intensity inside the PopZ condensates divided by the fluorescence intensity outside the condensates. A higher partitioning coefficient indicates stronger recruitment. Data shown for pentavalent (light green), pentavalent with IDR-156 (green), IDR-40 (light blue), wildtype (gray), and IDR-156 (blue). n equals 60 cells per strain. Two-sided student’s t-test; ns indicates no significant difference, two asterisks indicate p-value < 0.01, and four asterisks indicate p-value < 0.0001. Source data underlying graphs are provided in Source Data. f PopZ material properties affect the transcriptional program regulating asymmetry. Expression levels of CtrA activated genes sciP and pilA in cells expressing different PopZ mutants. Color code as in e. Three biological replicates (gray points), each with at least two technical replicates, were measured for each strain and each gene. Source data underlying graphs are provided in Source Data.
