AbstractPost-transcriptional regulation is a major level of gene expression control in any cell. In bacteria, multiprotein machines called RNA degradosomes are central for RNA processing and degradation and some were reported to be compartmentalized inside these organelle-less cells. The minimal RNA degradosome of the important gastric pathogen Helicobacter pylori is composed of the essential ribonuclease RNase J and RhpA, its sole DEAD-box RNA helicase, and plays a major role in the regulation of mRNA decay and adaptation to gastric colonization. Here, the subcellular localization of the H. pylori RNA degradosome was investigated using cellular fractionation and both confocal and super-resolution microscopy. We established that RNase J and RhpA are peripheral inner membrane proteins and that this association was mediated neither by ribosomes, by RNA nor by the RNase Y membrane protein. In live H. pylori cells, we observed that fluorescent RNase J and RhpA protein fusions assemble into non-polar foci. We identified factors that regulate the formation of these foci without affecting the degradosome membrane association. Flotillin, a bacterial membrane scaffolding protein, and free RNA promote foci formation in H. pylori. Finally, RNase J-GFP molecules and foci in cells were quantified by 3D-single-molecule fluorescence localization microscopy. The number and size of the RNase J foci were found to be scaled with growth phase and cell volume as was previously reported for eukaryotic ribonucleoprotein granules. In conclusion, we propose that membrane compartmentalization and the regulated clustering of RNase J-based degradosome hubs represent important levels of control of their activity and specificity.ImportanceHelicobacter pylori is a bacterial pathogen that chronically colonizes the stomach of half of the human population worldwide. Infection by H. pylori can lead to the development of gastric pathologies such as ulcers and adenocarcinoma, that causes up to 800.000 deaths in the world each year. Persistent colonization by H. pylori relies on regulation of the expression of adaptation-related genes. One major level of such control is post-transcriptional regulation that, in H. pylori, largely relies on a multi-protein molecular machine, an RNA-degradosome, that we previously discovered. In this study, we established that the two protein partners of this machine are associated to the membrane of H. pylori. Using cutting-edge microscopy, we showed that these complexes assemble into hubs whose formation is regulated by free RNA and scaled with bacterial size and growth phase. Cellular compartmentalization of molecular machines into hubs emerges as an important regulatory level in the organelle-less bacteria.
Differentially regulated orthologs in sorghum and the subgenomes of maize
