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The SMKbox riboswitch (also known as SAM-III) is an RNA element that regulates gene expression in bacteria. The SMK box
The SMKbox riboswitch (also known as SAM-III) is an RNA element that regulates gene expression in bacteria. The SMK box riboswitch
In molecular biology, a riboswitch is a regulatory segment of a messenger RNA molecule that binds a small molecule, resulting in a change in production of the proteins encoded by the mRNA. Thus, an mRNA that contains a riboswitch is directly invo ...
is found in the 5' UTR of the MetK gene in lactic acid bacteria
Lactobacillales are an order of gram-positive, low-GC, acid-tolerant, generally nonsporulating, nonrespiring, either rod-shaped ( bacilli) or spherical ( cocci) bacteria that share common metabolic and physiological characteristics. These bact ...
. 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.
Structure
The crystal structure of the riboswitch from ''E. faecalis'' was solved byX-ray crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
. The structure showed that the most conserved nucleotides involved in SAM binding were organised around a junction between three helices. In some species there are large insertions of up to 210 nucleotides within this structure.
See also
* SAH riboswitch * SAM-I riboswitch *SAM-II riboswitch
The SAM-II riboswitch is a RNA element found predominantly in Alphaproteobacteria that binds S-adenosyl methionine (SAM). Its structure and sequence appear to be unrelated to the SAM riboswitch found in Gram-positive bacteria. This SAM riboswit ...
* SAM-IV riboswitch
SAM-IV riboswitches are a kind of riboswitch that specifically binds S-adenosylmethionine (SAM), a cofactor used in many methylation reactions. Originally identified by bioinformatics, SAM-IV riboswitches are largely confined to the Actinomyce ...
* SAM-V riboswitch
* SAM-VI riboswitch
* SAM-Chlorobi RNA motif
* SAM–SAH riboswitch
References
External links
* Cis-regulatory RNA elements Riboswitch {{molecular-cell-biology-stub