Editorial: RNA Biology of Microorganisms

Israel Science Foundation 1274/19 Department of Science & Technology (India) Science Engineering Research Board (SERB), India EMR/2016/002247 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute of General Medical Sciences (NIGMS) R35GM136213 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 1190552Versión publicada - versión final del edito

The bacterial Sec system is required for the organization and function of the MreB cytoskeleton.

The Sec system is responsible for protein insertion, translocation and secretion across membranes in all cells. The bacterial actin homolog MreB controls various processes, including cell wall synthesis, membrane organization and polarity establishment. Here we show that the two systems genetically interact and that components of the Sec system, especially the SecA motor protein, are essential for spatiotemporal organization of MreB in E. coli, as evidenced by the accumulation of MreB at irregular sites in Sec-impaired cells. MreB mislocalization in SecA-defective cells significantly affects MreB-coordinated processes, such as cell wall synthesis, and induce formation of membrane invaginations enriched in high fluidity domains. Additionally, MreB is not recruited to the FtsZ ring in secA mutant cells, contributing to division arrest and cell filamentation. Our results show that all these faults are due to improper targeting of MreB to the membrane in the absence of SecA. Thus, when we reroute RodZ, MreB membrane-anchor, by fusing it to a SecA-independent integral membrane protein and overproducing it, MreB localization is restored and the defect in cell division is corrected. Notably, the RodZ moiety is not properly inserted into the membrane, strongly suggesting that it only serves as a bait for placing MreB around the cell circumference. Finally, we show that MreB localization depends on SecA also in C. crescentus, suggesting that regulation of MreB by the Sec system is conserved in bacteria. Taken together, our data reveal that the secretion system plays an important role in determining the organization and functioning of the cytoskeletal system in bacteria

BglG, the response regulator of the Escherichia coli bgl operon, is phosphorylated on a histidine residue.

We have shown previously that the activity of BglG, the response regulator of the bgl system, as a transcriptional antiterminator is modulated by the sensor BglF, which reversibly phosphorylates BglG. We show here that the phosphoryl group on BglG is present as a phosphoramidate, based on the sensitivity of phosphorylated BglG to heat, hydroxylamine, and acidic but not basic conditions. By analyzing the products of base-hydrolyzed phosphorylated BglG by thin-layer chromatography, we show that the phosphorylation occurs on a histidine residue. This result supports the notion that the bgl system is a member of a new family of bacterial sensory systems

BglF, the <i>Escherichia coli</i> β-Glucoside Permease and Sensor of the <i>bgl</i> System: Domain Requirements of the Different Catalytic Activities

ABSTRACT The Escherichia coli BglF protein, an enzyme II of the phosphoenolpyruvate-dependent carbohydrate phosphotransferase system, has several enzymatic activities. In the absence of β-glucosides, it phosphorylates BglG, a positive regulator of bgl operon transcription, thus inactivating BglG. In the presence of β-glucosides, it activates BglG by dephosphorylating it and, at the same time, transports β-glucosides into the cell and phosphorylates them. BglF is composed of two hydrophilic domains, IIA bgl and IIB bgl , and a membrane-bound domain, IIC bgl , which are covalently linked in the order IIBCA bgl . Cys-24 in the IIB bgl domain is essential for all the phosphorylation and dephosphorylation activities of BglF. We have investigated the domain requirement of the different functions carried out by BglF. To this end, we cloned the individual BglF domains, as well as the domain pairs IIBC bgl and IICA bgl , and tested which domains and which combinations are required for the catalysis of the different functions, both in vitro and in vivo. We show here that the IIB and IIC domains, linked to each other (IIBC bgl ), are required for the sugar-driven reactions, i.e., sugar phosphotransfer and BglG activation by dephosphorylation. In contrast, phosphorylated IIB bgl alone can catalyze BglG inactivation by phosphorylation. Thus, the sugar-induced and noninduced functions have different structural requirements. Our results suggest that catalysis of the sugar-induced functions depends on specific interactions between IIB bgl and IIC bgl which occur upon the interaction of BglF with the sugar. </jats:p