Journal
NUCLEIC ACIDS RESEARCH
Volume 47, Issue 13, Pages 6885-6899Publisher
OXFORD UNIV PRESS
DOI: 10.1093/nar/gkz494
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Funding
- Idaho State University
- Institutional Development Award from the National Institutes of General Medical Sciences [P20GM103408]
- National Institutes of General Medical Sciences [R35 GM118157, R01 GM042569-25S1, R01 GM127715]
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Maintaining manganese (Mn) homeostasis is important for the virulence of numerous bacteria. In the human respiratory pathogen Streptococcus pneu-moniae, the Mn-specific importer PsaBCA, exporter MntE, and transcriptional regulator PsaR establish Mn homeostasis. In other bacteria, Mn homeostasis is controlled by yybP-ykoY family riboswitches. Here, we characterize a yybP-ykoY family riboswitch upstream of the mgtA gene encoding a P-II-type ATPase in S. pneumoniae, suggested previously to function in Ca2+ efflux. We show that the mgtA riboswitch aptamer domain adopts a canonical yybP-ykoY structure containing a three-way junction that is compacted in the presence of Ca2+ or Mn2+ at a physiological Mg2+ concentration. Although Ca2+ binds to the RNA aptamer with higher affinity than Mn2+, in vitro activation of transcription read-through of mgtA by Mn2+ is much greater than by Ca2+. Consistent with this result, mgtA mRNA and protein levels increase approximate to 5-fold during cellular Mn stress, but only in genetic backgrounds of S. pneumoniae and Bacillus subtilis that exhibit Mn2+ sensitivity, revealing that this riboswitch functions as a failsafe 'on' signal to prevent Mn2+ toxicity in the presence of high cellular Mn2+. In addition, our results suggest that the S. pneumoniae yybP-ykoY riboswitch functions to regulate Ca2+ efflux under these conditions.
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