YkoK leader

The Ykok leader or M-box is a Mg²⁺-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.

ykoK leader
Predicted secondary structure and sequence conservation of ykoK
Identifiers
Symbol	ykoK
Rfam	RF00380
Other data
RNA type	Cis-reg; riboswitch
Domain(s)	Bacteria
SO	SO:0000233
PDB structures	PDBe

The Ykok leader was originally described as a conserved sequence with potential riboswitch function found upstream of the B. subtilis ykoK gene and genes with related functions in other bacteria.^[1] Examples of the conserved M-box RNA structure occur upstream of each of the three major families of Mg²⁺ transporters (CorA, MgtE and MgtA/MgtB) in various bacterial species.^[2]

The molecular structure of the M-box example upstream of the B. subtilis ykoK gene includes six bound Mg²⁺ ions. Biochemical studies indicate that this M-Box RNA compacts in the presence of Mg²⁺ and other divalent ions. This folding process appears to disrupt an antiterminator structure, and thereby allow a transcription terminator structure to form. As expected from this model, B. subtilis cells repress expression of a downstream reporter gene when grown in the presence of Mg²⁺. Therefore, the M-box appears to function as a genetic "off" switch that is important for maintaining Mg²⁺ homeostasis in bacteria.

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  A 3D representation of the Ykok leader. Structure of the M-box riboswitch aptamer domain from Bacillus subtilis.^[2]