Caulobacter crescentus RNase E condensation contributes to autoregulation and fitness

RNase E is the most common RNA decay nuclease in bacteria, setting the global mRNA decay rate and scaffolding formation of the RNA degradosome complex and BR-bodies. To properly set the global mRNA decay rate, RNase E from Escherichia coli and neighboring {gamma}-proteobacteria were found to autoregulate RNase E levels via the decay of its mRNAs 5 UTR. While the 5 UTR is absent from other groups of bacteria in the Rfam database, we identified that the -proteobacterium Caulobacter crescentus RNase E contains a similar 5 UTR structure that promotes RNase E autoregulation. In both bacteria, the C-terminal IDR of RNase E is required for proper autoregulation to occur, and this IDR is also necessary and sufficient for RNase E to phase-separate, generating BR-bodies. Using in vitro purified RNase E, we find that the IDRs ability to promote phase-separation correlates with enhanced 5 UTR cleavage, suggesting that phase-separation of RNase E with the 5 UTR enhances autoregulation. Finally, using growth competition experiments we find that a strain capable of autoregulation rapidly outcompetes a strain with a 5 UTR mutation that cannot autoregulate, suggesting autoregulation promotes optimal cellular fitness.