Hsp90 cis-regulatory element
The Hsp90 cis regulatory element is an RNA element (RNA thermometer) found in the 5' UTR of the Drosophila hsp90 mRNA. It is required for increased translational efficiency during the heat shock response. The hsp90 gene product is involved in the Drosophila heat shock response.
Source: Wikipedia — Hsp90 cis-regulatory element (CC BY-SA 4.0)