title: A Mg2+-responding RNA that controls the expression of a Mg2+ transporter.
abstract: Mg2+ is the most abundant divalent cation in biological systems. It is required for ATP-mediated enzymatic reactions and as a stabilizer of ribosomes and membranes. The enteric bacterium Salmonella enterica serovar Typhimurium harbors three Mg2+ transporters and a regulatory system-termed PhoP/PhoQ-whose activity is regulated by the extracytoplasmic levels of Mg2+. We have determined that expression of the PhoP-activated Mg2+ transporter MgtA is also controlled by its 5'-untranslated region (5'UTR). The 5'UTR of the mgtA gene can adopt different stem-loop structures depending on the Mg2+ levels, which determine whether transcription reads through into the mgtA-coding region or stops within the 5'UTR. This makes the mgtA 5'UTR the first example of a cation-responding riboswitch. The initiation of mgtA transcription responds to extracytoplasmic Mg2+, and its elongation into the coding region to cytoplasmic Mg2+, which provides a singular example where the same ligand is sensed in different cellular compartments to regulate disparate steps in gene transcription. The PhoP-activated Mg2+ transporter mgtB is also regulated by Mg2+ in a strain lacking the Mg2+ sensor PhoQ, suggesting the presence of additional Mg2+-responding devices.
authors: Department of Molecular Microbiology, Washington University School of Medicine, Howard Hughes Medical Institute, St. Louis, Missouri 63110, USA.
authors: E A
authors: EA
authors: Groisman
authors: M J
authors: MJ
authors: Cromie
authors: Y
authors: Y
authors: Shi
authors: T
authors: T
authors: Latifi
mesh_terms: D020121:5' Untranslated Regions; D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology*; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; C079792:PhoQ protein, Bacteria; D012329:RNA, Bacterial; D012333:RNA, Messenger; C061064:PhoP protein, Bacteria; D000251:Adenosine Triphosphatases; C093585:MgtA protein, bacteria; D008274:Magnesium