The hairpin ribozyme is a small section of RNA that can act as a ribozyme. Like the hammerhead ribozyme it is found in RNA satellites of plant viruses. It was first identified in the minus strand of the tobacco ringspot virus (TRSV) satellite RNA where it catalyzes self-cleavage and joining (ligation) reactions to process the products of rolling circle virus replication into linear and circular satellite RNA molecules. The hairpin ribozyme is similar to the hammerhead ribozyme in that it does not require a metal ion for the reaction. Biological function The hairpin ribozyme is an RNA motif that catalyzes RNA processing reactions essential for replication of the satellite RNA molecules in which it is embedded. These reactions are self-processing, i.e. a molecule rearranging its own structure. Both cleavage and end joining reactions are mediated by the ribozyme motif, leading to a mixture of interconvertible linear and circular satellite RNA molecules. These reactions are important for processing the large multimeric RNA molecules that are generated by rolling circle replication. At the end of the replication cycle, these large intermediates of satellite RNA replication are processed down to unit length molecules (circular or linear) before they can be packaged by viruses and carried to other cells for further rounds of replication. Natural versions of the hairpin ribozyme In the 1980s, the hairpin ribozyme was identified in 3 naturally occurring and well-characterized sequences: satellite RNA of tobacco ringspot virus (sTRSV) satellite RNA of chicory yellow mottle virus (sCYMV) satellite RNA of arabis mosaic virus (sARMV) Later work in 2021 revealed almost 1000 hairpin ribozyme sequences in largely unknown organisms found in metatranscriptome data. These newer sequences were hypothesized to occur in organisms that, like those containing the three previously found hairpin ribozymes, use single-stranded, circular RNA genomes. The circularity of the genomes was supported experimentally, but the further nature of the organisms is not yet well studied. Artificial versions of the hairpin ribozyme Smaller artificial versions of the hairpin ribozyme have been developed to enable a more detailed experimental analysis of the molecule. This is a commonly used strategy for separating those parts of a self-processing RNA molecule that are essential for the RNA processing reactions from those parts which serve unrelated functions. Through this process, a 50 nucleotide minimal catalytic domain and a 14 nucleotide substrate were identified. Using these artificially derived sequences, a trans-acting ribozyme was developed that can catalyze