RNase E biomolecular condensates stimulate PNPase activity

Bacterial Ribonucleoprotein bodies (BR-bodies) play an essential role in organizing RNA degradation via liquid-liquid phase separation in the cytoplasm of bacteria. BR-bodies mediate multi-step mRNA decay through the concerted activity of the endoribonuclease RNase E coupled with the 3-5 exonuclease Polynucleotide Phosphorylase (PNPase). Our past in vivo studies indicated that the loss of PNPase recruitment into BR-bodies led to a significant build-up of RNA decay intermediates in Caulobacter crescentus. We reconstituted RNase Es C-terminal domain together with PNPase to understand how RNase E biomolecular condensates can tailor the functions of PNPase. We found that PNPase catalytic activity is accelerated when colocalized with the RNase E biomolecular condensates. In contrast, disruption of the RNase E-PNPase protein-protein interaction led to a loss of PNPase recruitment into the BR-bodies and a loss of ribonuclease rate enhancement. We also found that BR-bodies could enhance the decay of select RNA substrates, as we observed a 3.4-fold enhancement of polyadenylic acid (poly(A)) degradation and no impact upon poly(U) degradation. Our investigation into the origins of the 3.4-fold rate enhancement for poly(A) decay indicates a combination of scaffolding and mass action effects impact due to the concentrated biomolecular condensate environment accelerating RNA decay. Consistent with our past in vivo work, these studies suggest BR-bodies are sites of accelerated RNA decay that can shape the available transcriptome.