Riboswitch Mechanism
RNA that senses small molecules and controls its own gene expression
TPP Riboswitch
SAM Riboswitch
Adenine Riboswitch
Control
Ligand concentration
0 µM (no ligand)
GENE ON
(no ligand)
OFF-switch: ligand represses expression
Current:
TPP Riboswitch
The
thiamine pyrophosphate (TPP)
riboswitch is the most widespread in bacteria. Found in thiC, thiM and other thiamine biosynthesis genes.
Aptamer domain
binds TPP with ~100 nM affinity (Kd). TPP binding induces a conformational change in the
expression platform
— an intrinsic terminator forms, halting transcription.
Feedback loop: high TPP → riboswitch OFF → less TPP made → TPP falls → riboswitch ON.
Riboswitch Classes
~30+
confirmed riboswitch classes.
Most common in bacteria; some in eukaryotes.
Mechanisms:
• Transcription termination (rho-independent)
• Translation inhibition (SD sequestration)
• Ribozyme activation (GlmS)
• Splicing control (eukaryotic TPP)