Two recent reports demonstrate that in vivo selection can isolate novel RNAs that activate transcription when tethered to a gene promoter. This highlights the structural plasticity that allows RNA to fulfill many functions normally carried out by proteins.
Gottesfeld, J. M., & Barbas, C. F. (2003, July 1). RNA as a transcriptional activator. Chemistry and Biology. Elsevier Ltd. https://doi.org/10.1016/S1074-5521(03)00153-4