Tag:PP7 represents an RNA hairpin loop that is specifically bound by the PP7 bacteriophage coat protein (Tag:PCP). In addition, the Tag:PP7 sequence has been designed so that it can be translated. Tag:PP7 and Tag:PCP are designed to be used as a RNA biosensor, which allows untranslated mRNAs to be distinguished from those that have undergone a round of translation. Prior to translation, a mRNA containing Tag:PP7 sequences can be bound by a reporter protein with a functional readout (such as fluorescence, bioluminescence or enzymatic activity) fused to Tag:PCP. During the first round of translation, this reporter protein containing Tag:PCP is knocked off the mRNA by the ribosome. This property can be utilised to study the dynamics of translation, for example as part of the 'TRICK' (translating RNA imaging by coat protein knockoff) technique to distinguish untranslated mRNAs from ones that have undergone a round of translation (FBrf0232471).