IbpB thermometer

The IbpB thermometer is an RNA thermometer element found in the ibpAB operon.^[1] The operon contains two heat-shock genes, encoding inclusion body binding proteins A and B (IbpA/B), and is the most drastically upregulated operon under heat-shock in Escherichia coli.^[2]

IbpB thermometer
Conserved secondary structure of the IbpB thermometer
Identifiers
Symbol	ibpB 5' UTR
Other data
RNA type	RNA thermometer
Domain(s)	E. coli
PDB structures	PDBe

IbpA is regulated by a ROSE element found in its 5' UTR,^[3][4] while IbpB has its own heat-sensitive cis-regulatory element. The activity of this thermoregulator was confirmed in vitro but was not found in vivo, suggesting more complicated operon regulation exists in bacterial cells.^[1]

IbpB protein

The IbpB protein, whose expression is regulated by the IbpB thermometer, is 48% identical to IbpA (at the level of amino acid sequence) yet fulfils a different role in heat shock. When IbpB is absent, IbpA protein will form long fibrils which is unusual for a heat shock protein; IbpB, acting as a co-chaperone, inhibits IbpA from forming this structure.^[5]

Under heat shock, IbpB protein dissociates to give two smaller subunits and also rearranges its tertiary structure.^[6] This "remarkable conformational transformation"^[7] is thought to be essential for IbpB to act as a co-chaperone with IbpA under heat shock.^[8]

IbpB has been found to retain active for a significant time after a heat shock stimulus has been removed.^[7]