SMK box translational riboswitch
A representation of the SMK box translational riboswitch secondary structure including a colour scheme that indicates the degree of sequence conservation.
Identifiers
Symbol	SMK_box_riboswitch
Alt. Symbols	SAM-III, SMK
Rfam	RF01767
Other data
RNA type	Riboswitch
Domain(s)	Bacillota
PDB structures	PDBe 3e5f 3e5e 3e5c

The S_MKbox riboswitch (also known as SAM-III) is an RNA element that regulates gene expression in bacteria.^[2][3] The S_MK box riboswitch is found in the 5' UTR of the MetK gene in lactic acid bacteria. The structure of this element changes upon binding to S-adenosyl methionine (SAM) to a conformation that blocks the shine-dalgarno sequence and blocks translation of the gene.

There are other known SAM-binding riboswitches such as SAM-I and SAM-II, but these appear to share no similarity in sequence or structure to SAM-III.

The crystal structure of the riboswitch from E. faecalis was solved by X-ray crystallography. The structure showed that the most conserved nucleotides involved in SAM binding were organised around a junction between three helices.^[1] In some species there are large insertions of up to 210 nucleotides within this structure.

• SAH riboswitch
• SAM-I riboswitch
• SAM-II riboswitch
• SAM-IV riboswitch
• SAM-V riboswitch
• SAM-VI riboswitch
• SAM-Chlorobi RNA motif
• SAM–SAH riboswitch

• Page for SMK box translational riboswitch at Rfam

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