Illustration of RNA (ribonucleic acid) obelisks beside a bacterium (bottom). RNA obelisks are viroid-like fragments of RNA that have been found replicating within bacteria in the human mouth and gut. They are formed of single-stranded circular RNA and have a rod-like secondary structure. The function of the proteins obelisks code for is not known. If they impact their bacterial hosts, it is possible that they could in turn impact human health.