Electron microscopic evidence for the circular form of RNA in the cytoplasm of eukaryotic cells

LINEAR single-stranded RNA genomes extracted from several RNA viruses were found to exist in a circular conformation when examined in the electron microscope in partially denaturing conditions1–4. The circular conformation of viral RNA presumably arises from base pairing between RNA sequences at the two ends of the RNA molecules. The biological significance of the circular structure of single-stranded RNA is still unknown. Here we report the observation of the circular form of RNA extracted from the cytoplasm of several eukaryotic cells.