The Ykok leader or M-box is a Mg
2+-sensing
RNA structure that controls the
expression of
Magnesium ion transport proteins in bacteria. It is a distinct structure to the
Magnesium responsive RNA element The Magnesium responsive RNA element, not to be confused with the completely distinct M-box riboswitch, is a cis-regulatory element that regulates the expression of the magnesium transporter protein MgtA. It is located in the 5' UTR of this gene. ...
.
The Ykok leader was originally described as a
conserved sequence with potential
riboswitch function found
upstream
Upstream may refer to:
* Upstream (bioprocess)
* ''Upstream'' (film), a 1927 film by John Ford
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of the ''
B. subtilis
''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillus' ...
'' ykoK gene and genes with related functions in other bacteria.
Examples of the conserved M-box RNA structure occur upstream of each of the three major families of Mg
2+ transporters (CorA, MgtE and MgtA/MgtB) in various bacterial species.
The molecular structure of the M-box example upstream of the ''
B. subtilis
''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillus' ...
'' ykoK gene includes six bound Mg
2+ ions. Biochemical studies indicate that this M-Box RNA compacts in the presence of Mg
2+ and other
divalent ions. This folding process appears to disrupt an antiterminator structure, and thereby allow a
transcription terminator
In genetics, a transcription terminator is a section of nucleic acid sequence that marks the end of a gene or operon in genomic DNA during transcription. This sequence mediates transcriptional termination by providing signals in the newly synthe ...
structure to form. As expected from this model, ''B. subtilis'' cells repress expression of a downstream reporter gene when grown in the presence of Mg
2+. Therefore, the M-box appears to function as a genetic "off" switch that is important for maintaining Mg
2+ homeostasis
In biology, homeostasis (British English, British also homoeostasis) Help:IPA/English, (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. Thi ...
in bacteria.
File:Magnesium_sensor_RNA_pdb-2qbz.png , A 3D representation of the Ykok leader. Structure of the M-box riboswitch aptamer domain from Bacillus subtilis.
References
External links
*
Protein Data Bank: M-Box Structure
Cis-regulatory RNA elements
Riboswitch
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