NPG Nature Microbiology Reviews ions toxic metal potentially levels of intracellular … balancethe riboswitches metal-sensing transition selective NATURE REVIEWS REVIEWS NATURE |

MICROBIOLOGY yybP past In decade. its ligand unclear has for been the transport; however, identity the of are predicted to have arole incation characterized downstream genes genomes,in bacterial and poorly riboswitch is widely distributed or . The controllingally either transcription alters mRNA the structure, gener ligandof to riboswitch aspecific the regioncoding of mRNAs; binding structures located upstream of the ionmetal transporters. ions to regulate expression the of selectively bind to transition metal involveswhich riboswitches that of transition ion metal homeostasis, of mode anew identify regulation transporters. Three studies new now expressionthe of corresponding the metal-sensing that regulate homeostasis is tightly controlled by to toxicity. their Therefore, ion metal athreat cells owingpose to bacterial ever, at concentrations, high they of proteins and nucleic acids; how cofactors and components structural Transition ions metal are essential Metalloregulatory riboswitches tion of astem–loop structure that riboswitch that prevent forma the inducesthis changes structural inthe switch, directly which binds to Mn is regulated by the mntP binds H-NS,which to the sive of nucleoid-binding the effects MntR and Fur antagonize repres the transcription the because factors levels. transcriptional and translational is induced by Mn Dambach a manganese (Mn waswhich recently shown to encode 5ʹ UTRin the of the

Riboswitches are regulatory RNA BACTERIAL GENETICS

| ‑ AOP, published online 13April 2015;doi:10.1038/nrmicro3478 promoter. MntP translation ykoY mntP et al.

riboswitch is located transcription is activated showed that MntP Escherichia coli Escherichia 2+ 2+ yybP-ykoY yybP-ykoY ) exporter. at the both mntP © 2015 Macmillan Publishers Limited. Allrights reserved gene, gene,

ribo , the the , - - - ­ 2+ - ; have roles homeostasis. in metal switch of downstream genes that functions as an Mn Mn inducedmotif by are specifically also subtilis initiation. Other of site sequesters ribosome-binding the tion of terminator the structure and L1–L3 interface, resulting indisrup Mn riboswitch,in the whereas ahigh of apremature terminator structure concentration to leads formation the transcriptional level: a low Mn regulates gene expression at the that the observations, authors the propose mational changes. on these Based L1–L3interfacethe owing to confor thatrevealed removal of Mn for Mn tive and second the site selec is highly site has low metal-binding specificity modates two metal-binding sites: one two loops accom these face between loops, L1and termed L3.The inter interaction two conserved between junction and hand-shaking adistal by of two sets contacts: afour-way pin structure and are held inplace stacked helicescoaxially form ahair resolution and report that of two sets ligand-sensingthe domain) at 2.85 riboswitch domain is (which Mn the structure of crystal the determined scriptional readthrough. The authors concentrations of Mn terminated transcripts, whereas high Mn affinity.with high In absence the of encoding found upstream of ATPase- the yybP-ykoY showed thatthe mntP In agreement withPrice this, 2+ 2+ 2+ , suggesting that riboswitch the concentration stabilizes the , RNA polymerase produces genes that have the 2+ and thus enables translation L. lactis -bound yoaB riboswitch, is which 2+ . Additional structures gene, binds Mn

yybP-ykoY Lactococcus lactis Lactococcus E. coli L. lactis 2+ RESEARCH HIGHLIGHTS -sensing ‘on’ 2+ and and lead to lead tran

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class in anovelidentified structured RNA functions as an Mn (a riboswitch-controlled protein) genome, suggesting that its product L. lactis subtilis B. potentially toxic ions. metal intracellularbalance the levels of tion metal-sensing riboswitches to transi selective that use homeostasis. selectively regulate transition metal NiCo that riboswitches notion the Zn or binding Co of several clustering facilitates cooperative sites. The authors propose that this Co clustered interhelical forming with helices of stacked sets coaxially of ribo these crystallography studies X-ray efflux. involved incobalt, zinc and cadmium czcD riboswitchesare located upstream of and (Ni abundance ions metal (Co binds and responds to low- the growth inhibition of aMn transcriptional readthrough. Finally, in the presencein the of Ni a putative cationinduced was exporter riboswitch- Finally, authors the found that aNiCo by riboswitch the aptamer domain. Dambach, M. ORIGINAL RESEARCHPAPERS 57 expression of heavy metal transporters. cooperatively bindNi (2015) ykoY Price, I. R. element. riboswitch isamanganese-responsive regulatory , 1088–1098(2015) In athird study, Furukawa In summary, data these suggest orphan riboswitches. genes, which encode proteins proteins genes, encode which 2+ | Furukawa, K. had no effect, supporting had no effect,

Clostridiales Mol. Cell yoaB et al. strain was rescued when strain when was rescued et al. Mn otiig ee encoding gene ­containing switches two revealed ­ 2+ was integrated into the

57 Theubiquitous 2+ - or Ni 2+ VOLUME 13 -sensing mechanismsof , 1099–1109(2015) et al. ). These NiCo ). These 2+ orCo Bacterial riboswitches Bacterialriboswitches 2+ Mol. Cell that selectively 2+ 2+ exporter. 2+ 2+ , whereas Mn ionsandcontrol -binding or Ni or Andrea Toit Du

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