SAM riboswitch (S-box leader)

Not to be confused with SAM–SAH riboswitch.
SAM riboswitch (S-box leader)
Predicted secondary structure and sequence conservation of SAM riboswitch (S box leader)
Identifiers
SymbolSAM
Alt. SymbolsS_box
RfamRF00162 CL00012
Other data
RNA typeCis-reg; riboswitch
Domain(s)Bacteria
GOGO:0010468
SOSO:0000035
PDB structuresPDBe
SAM-I-IV-variant
Consensus secondary structure and sequence conservation of SAM-I/IV variant riboswitch
Identifiers
SymbolSAM-I-IV-variant
RfamRF01725
Other data
RNA type Cis-reg; Riboswitch
GOGO:0010468,GO:0046500
SOSO:0000035
PDB structuresPDBe

The SAM riboswitch (also known as the S-box leader and the SAM-I riboswitch) is found upstream of a number of genes which code for proteins involved in methionine or cysteine biosynthesis in Gram-positive bacteria. Two SAM riboswitches in Bacillus subtilis that were experimentally studied act at the level of transcription termination control. The predicted secondary structure consists of a complex stem-loop region followed by a single stem-loop terminator region. An alternative and mutually exclusive form involves bases in the 3' segment of helix 1 with those in the 5' region of helix 5 to form a structure termed the anti-terminator form.[1][2][3] When SAM is unbound, the anti-terminator sequence sequesters the terminator sequence so the terminator is unable to form, allowing the polymerase to read-through the downstream gene.[4] When S-Adenosyl methionine (SAM) is bound to the aptamer, the anti-terminator is sequestered by an anti-anti-terminator; the terminator forms and terminates the transcription.[4][5] However, many SAM riboswitches are likely to regulate gene expression at the level of translation.

  1. ^ Grundy FJ, Henkin TM (1998). "The S box regulon: a new global transcription termination control system for methionine and cysteine biosynthesis genes in gram-positive bacteria". Mol. Microbiol. 30 (4): 737–749. doi:10.1046/j.1365-2958.1998.01105.x. PMID 10094622.
  2. ^ Epshtein, V; Mironov AS; Nudler E (2003). "The riboswitch-mediated control of sulfur metabolism in bacteria". Proc Natl Acad Sci USA. 100 (9): 5052–5056. Bibcode:2003PNAS..100.5052E. doi:10.1073/pnas.0531307100. PMC 154296. PMID 12702767.
  3. ^ Winkler WC, Nahvi A, Sudarsan N, Barrick JE, Breaker RR (2003). "An mRNA structure that controls gene expression by binding S-adenosylmethionine". Nat. Struct. Biol. 10 (9): 701–707. doi:10.1038/nsb967. PMID 12910260. S2CID 21951110.
  4. ^ a b Winkler, W., Nahvi, A., Sudarsan, N., Barrick, J., and Breaker, R. (2003) An mRNA structure that controls gene expression by binding S-adenosylmethionine. Nature Structural Biology, 10(9), 701–707.
  5. ^ Epshtein, V., Mironov, A., and Nudler, E. (2003) The riboswitch-mediated control of sulfur metabolism in bacteria. Proceedings of the National Academy of Sciences of the USA, 100, 5052–5056.