Journal
NATURE
Volume 432, Issue 7015, Pages 411-415Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/nature03037
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Funding
- NIGMS NIH HHS [T32 GM008759, T32 GM142607] Funding Source: Medline
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Riboswitches are genetic regulatory elements found in the 50 untranslated region of messenger RNA that act in the absence of protein cofactors(1,2). They are broadly distributed across bacteria and account for the regulation of more than 2% of all genes in Bacillus subtilis, underscoring their importance in the control of cellular metabolism(3). The 5' untranslated region of many mRNAs of genes involved in purine metabolism and transport contain a guanine-responsive riboswitch that directly binds guanine, hypoxanthine or xanthine to terminate transcription(3,4). Here we report the crystal structure at 1.95 Angstrom resolution of the purine-binding domain of the guanine riboswitch from the xpt-pbuX operon of B. subtilis bound to hypoxanthine, a prevalent metabolite in the bacterial purine salvage pathway. This structure reveals a complex RNA fold involving several phylogenetically conserved nucleotides that create a binding pocket that almost completely envelops the ligand. Hypoxanthine functions to stabilize this structure and to promote the formation of a downstream transcriptional terminator element, thereby providing a mechanism for directly repressing gene expression in response to an increase in intracellular concentrations of metabolite.
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