Where would you find a Riboswitch?

The correct answer will be - in the 5' untranslated region of prokaryotic mRNA.

Explanation:

Riboswitches are the cis-regulatory RNA elements present in the non-coding segment of the mRNA. The riboswitches are common in prokaryotes but research showed that they are also present in the few eukaryotes. They are located in the non-coding 5' untranslated region of prokaryotic mRNA.

The riboswitches are usually made of 35 to 200 nucleotides which can bind to co-enzymes, small molecules and metabolites and change their conformation to regulated gene expression.

Thus, in the 5' untranslated region of prokaryotic mRNA is the correct answer.